minix/servers/vfs/link.c

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/* This file handles the LINK and UNLINK system calls. It also deals with
* deallocating the storage used by a file when the last UNLINK is done to a
* file and the blocks must be returned to the free block pool.
*
* The entry points into this file are
* do_link: perform the LINK system call
* do_unlink: perform the UNLINK and RMDIR system calls
* do_rename: perform the RENAME system call
* do_truncate: perform the TRUNCATE system call
* do_ftruncate: perform the FTRUNCATE system call
* do_rdlink: perform the RDLNK system call
*/
#include "fs.h"
#include <sys/stat.h>
#include <string.h>
#include <minix/com.h>
#include <minix/callnr.h>
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#include <minix/vfsif.h>
#include <sys/dirent.h>
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#include <assert.h>
#include "file.h"
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#include "path.h"
#include "vnode.h"
#include "scratchpad.h"
/*===========================================================================*
* do_link *
*===========================================================================*/
int do_link(void)
{
/* Perform the link(name1, name2) system call. */
int r = OK;
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struct vnode *vp = NULL, *dirp = NULL;
struct vmnt *vmp1 = NULL, *vmp2 = NULL;
char fullpath[PATH_MAX];
struct lookup resolve;
vir_bytes vname1, vname2;
size_t vname1_length, vname2_length;
vname1 = job_m_in.m_lc_vfs_link.name1;
vname1_length = job_m_in.m_lc_vfs_link.len1;
vname2 = job_m_in.m_lc_vfs_link.name2;
vname2_length = job_m_in.m_lc_vfs_link.len2;
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lookup_init(&resolve, fullpath, PATH_NOFLAGS, &vmp1, &vp);
resolve.l_vmnt_lock = VMNT_WRITE;
resolve.l_vnode_lock = VNODE_READ;
/* See if 'name1' (file to be linked to) exists. */
if (fetch_name(vname1, vname1_length, fullpath) != OK) return(err_code);
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if ((vp = eat_path(&resolve, fp)) == NULL) return(err_code);
/* Does the final directory of 'name2' exist? */
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lookup_init(&resolve, fullpath, PATH_NOFLAGS, &vmp2, &dirp);
resolve.l_vmnt_lock = VMNT_READ;
resolve.l_vnode_lock = VNODE_WRITE;
if (fetch_name(vname2, vname2_length, fullpath) != OK)
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r = err_code;
else if ((dirp = last_dir(&resolve, fp)) == NULL)
r = err_code;
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if (r != OK) {
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unlock_vnode(vp);
unlock_vmnt(vmp1);
put_vnode(vp);
return(r);
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}
/* Check for links across devices. */
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if (vp->v_fs_e != dirp->v_fs_e)
r = EXDEV;
else
r = forbidden(fp, dirp, W_BIT | X_BIT);
if (r == OK)
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r = req_link(vp->v_fs_e, dirp->v_inode_nr, fullpath,
vp->v_inode_nr);
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unlock_vnode(vp);
unlock_vnode(dirp);
if (vmp2 != NULL) unlock_vmnt(vmp2);
unlock_vmnt(vmp1);
put_vnode(vp);
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put_vnode(dirp);
return(r);
}
/*===========================================================================*
* do_unlink *
*===========================================================================*/
int do_unlink(void)
{
/* Perform the unlink(name) or rmdir(name) system call. The code for these two
* is almost the same. They differ only in some condition testing. Unlink()
* may be used by the superuser to do dangerous things; rmdir() may not.
* The syscall might provide 'name' embedded in the message.
*/
struct vnode *dirp, *dirp_l, *vp;
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struct vmnt *vmp, *vmp2;
int r;
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char fullpath[PATH_MAX];
struct lookup resolve, stickycheck;
if (copy_path(fullpath, sizeof(fullpath)) != OK)
return(err_code);
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lookup_init(&resolve, fullpath, PATH_RET_SYMLINK, &vmp, &dirp_l);
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resolve.l_vmnt_lock = VMNT_WRITE;
resolve.l_vnode_lock = VNODE_WRITE;
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/* Get the last directory in the path. */
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if ((dirp = last_dir(&resolve, fp)) == NULL) return(err_code);
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/* Make sure that the object is a directory */
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if (!S_ISDIR(dirp->v_mode)) {
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unlock_vnode(dirp);
unlock_vmnt(vmp);
put_vnode(dirp);
return(ENOTDIR);
}
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/* The caller must have both search and execute permission */
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if ((r = forbidden(fp, dirp, X_BIT | W_BIT)) != OK) {
unlock_vnode(dirp);
unlock_vmnt(vmp);
put_vnode(dirp);
return(r);
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}
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/* Also, if the sticky bit is set, only the owner of the file or a privileged
user is allowed to unlink */
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if ((dirp->v_mode & S_ISVTX) == S_ISVTX) {
/* Look up inode of file to unlink to retrieve owner */
lookup_init(&stickycheck, resolve.l_path, PATH_RET_SYMLINK, &vmp2, &vp);
stickycheck.l_vmnt_lock = VMNT_READ;
stickycheck.l_vnode_lock = VNODE_READ;
vp = advance(dirp, &stickycheck, fp);
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assert(vmp2 == NULL);
if (vp != NULL) {
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if (vp->v_uid != fp->fp_effuid && fp->fp_effuid != SU_UID)
r = EPERM;
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unlock_vnode(vp);
put_vnode(vp);
} else
r = err_code;
if (r != OK) {
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unlock_vnode(dirp);
unlock_vmnt(vmp);
put_vnode(dirp);
return(r);
}
}
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VFS: fix locking bugs .sync and fsync used unnecessarily restrictive locking type .fsync violated locking order by obtaining a vmnt lock after a filp lock .fsync contained a TOCTOU bug .new_node violated locking rules (didn't upgrade lock upon file creation) .do_pipe used unnecessarily restrictive locking type .always lock pipes exclusively; even a read operation might require to do a write on a vnode object (update pipe size) .when opening a file with O_TRUNC, upgrade vnode lock when truncating .utime used unnecessarily restrictive locking type .path parsing: .always acquire VMNT_WRITE or VMNT_EXCL on vmnt and downgrade to VMNT_READ if that was what was actually requested. This prevents the following deadlock scenario: thread A: lock_vmnt(vmp, TLL_READSER); lock_vnode(vp, TLL_READSER); upgrade_vmnt_lock(vmp, TLL_WRITE); thread B: lock_vmnt(vmp, TLL_READ); lock_vnode(vp, TLL_READSER); thread A will be stuck in upgrade_vmnt_lock and thread B is stuck in lock_vnode. This happens when, for example, thread A tries create a new node (open.c:new_node) and thread B tries to do eat_path to change dir (stadir.c:do_chdir). When the path is being resolved, a vnode is always locked with VNODE_OPCL (TLL_READSER) and then downgraded to VNODE_READ if read-only is actually requested. Thread A locks the vmnt with VMNT_WRITE (TLL_READSER) which still allows VMNT_READ locks. Thread B can't acquire a lock on the vnode because thread A has it; Thread A can't upgrade its vmnt lock to VMNT_WRITE (TLL_WRITE) because thread B has a VMNT_READ lock on it. By serializing vmnt locks during path parsing, thread B can only acquire a lock on vmp when thread A has completely finished its operation.
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upgrade_vmnt_lock(vmp);
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if (job_call_nr == VFS_UNLINK)
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r = req_unlink(dirp->v_fs_e, dirp->v_inode_nr, fullpath);
else
r = req_rmdir(dirp->v_fs_e, dirp->v_inode_nr, fullpath);
unlock_vnode(dirp);
unlock_vmnt(vmp);
put_vnode(dirp);
return(r);
}
/*===========================================================================*
* do_rename *
*===========================================================================*/
int do_rename(void)
{
/* Perform the rename(name1, name2) system call. */
int r = OK, r1;
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struct vnode *old_dirp = NULL, *new_dirp = NULL, *new_dirp_l = NULL, *vp;
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struct vmnt *oldvmp, *newvmp, *vmp2;
char old_name[PATH_MAX];
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char fullpath[PATH_MAX];
struct lookup resolve, stickycheck;
vir_bytes vname1, vname2;
size_t vname1_length, vname2_length;
vname1 = job_m_in.m_lc_vfs_link.name1;
vname1_length = job_m_in.m_lc_vfs_link.len1;
vname2 = job_m_in.m_lc_vfs_link.name2;
vname2_length = job_m_in.m_lc_vfs_link.len2;
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lookup_init(&resolve, fullpath, PATH_RET_SYMLINK, &oldvmp, &old_dirp);
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/* Do not yet request exclusive lock on vmnt to prevent deadlocks later on */
resolve.l_vmnt_lock = VMNT_WRITE;
resolve.l_vnode_lock = VNODE_WRITE;
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/* See if 'name1' (existing file) exists. Get dir and file inodes. */
if (fetch_name(vname1, vname1_length, fullpath) != OK) return(err_code);
if ((old_dirp = last_dir(&resolve, fp)) == NULL) return(err_code);
/* If the sticky bit is set, only the owner of the file or a privileged
user is allowed to rename */
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if ((old_dirp->v_mode & S_ISVTX) == S_ISVTX) {
/* Look up inode of file to unlink to retrieve owner */
lookup_init(&stickycheck, resolve.l_path, PATH_RET_SYMLINK, &vmp2, &vp);
stickycheck.l_vmnt_lock = VMNT_READ;
stickycheck.l_vnode_lock = VNODE_READ;
vp = advance(old_dirp, &stickycheck, fp);
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assert(vmp2 == NULL);
if (vp != NULL) {
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if(vp->v_uid != fp->fp_effuid && fp->fp_effuid != SU_UID)
r = EPERM;
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unlock_vnode(vp);
put_vnode(vp);
} else
r = err_code;
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if (r != OK) {
unlock_vnode(old_dirp);
unlock_vmnt(oldvmp);
put_vnode(old_dirp);
return(r);
}
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}
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/* Save the last component of the old name */
if (strlen(fullpath) >= sizeof(old_name)) {
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unlock_vnode(old_dirp);
unlock_vmnt(oldvmp);
put_vnode(old_dirp);
return(ENAMETOOLONG);
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}
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strlcpy(old_name, fullpath, PATH_MAX);
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/* See if 'name2' (new name) exists. Get dir inode */
lookup_init(&resolve, fullpath, PATH_RET_SYMLINK, &newvmp, &new_dirp_l);
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resolve.l_vmnt_lock = VMNT_READ;
resolve.l_vnode_lock = VNODE_WRITE;
if (fetch_name(vname2, vname2_length, fullpath) != OK) r = err_code;
else if ((new_dirp = last_dir(&resolve, fp)) == NULL) r = err_code;
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/* We used a separate vnode pointer to see whether we obtained a lock on the
* new_dirp vnode. If the new directory and old directory are the same, then
* the VNODE_WRITE lock on new_dirp will fail. In that case, new_dirp_l will
* be NULL, but new_dirp will not.
*/
if (new_dirp == old_dirp) assert(new_dirp_l == NULL);
if (r != OK) {
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unlock_vnode(old_dirp);
unlock_vmnt(oldvmp);
put_vnode(old_dirp);
return(r);
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}
/* Both parent directories must be on the same device. */
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if (old_dirp->v_fs_e != new_dirp->v_fs_e) r = EXDEV;
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/* Parent dirs must be writable, searchable and on a writable device */
if ((r1 = forbidden(fp, old_dirp, W_BIT|X_BIT)) != OK ||
(r1 = forbidden(fp, new_dirp, W_BIT|X_BIT)) != OK) r = r1;
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if (r == OK) {
VFS: fix locking bugs .sync and fsync used unnecessarily restrictive locking type .fsync violated locking order by obtaining a vmnt lock after a filp lock .fsync contained a TOCTOU bug .new_node violated locking rules (didn't upgrade lock upon file creation) .do_pipe used unnecessarily restrictive locking type .always lock pipes exclusively; even a read operation might require to do a write on a vnode object (update pipe size) .when opening a file with O_TRUNC, upgrade vnode lock when truncating .utime used unnecessarily restrictive locking type .path parsing: .always acquire VMNT_WRITE or VMNT_EXCL on vmnt and downgrade to VMNT_READ if that was what was actually requested. This prevents the following deadlock scenario: thread A: lock_vmnt(vmp, TLL_READSER); lock_vnode(vp, TLL_READSER); upgrade_vmnt_lock(vmp, TLL_WRITE); thread B: lock_vmnt(vmp, TLL_READ); lock_vnode(vp, TLL_READSER); thread A will be stuck in upgrade_vmnt_lock and thread B is stuck in lock_vnode. This happens when, for example, thread A tries create a new node (open.c:new_node) and thread B tries to do eat_path to change dir (stadir.c:do_chdir). When the path is being resolved, a vnode is always locked with VNODE_OPCL (TLL_READSER) and then downgraded to VNODE_READ if read-only is actually requested. Thread A locks the vmnt with VMNT_WRITE (TLL_READSER) which still allows VMNT_READ locks. Thread B can't acquire a lock on the vnode because thread A has it; Thread A can't upgrade its vmnt lock to VMNT_WRITE (TLL_WRITE) because thread B has a VMNT_READ lock on it. By serializing vmnt locks during path parsing, thread B can only acquire a lock on vmp when thread A has completely finished its operation.
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upgrade_vmnt_lock(oldvmp); /* Upgrade to exclusive access */
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r = req_rename(old_dirp->v_fs_e, old_dirp->v_inode_nr, old_name,
new_dirp->v_inode_nr, fullpath);
}
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unlock_vnode(old_dirp);
unlock_vmnt(oldvmp);
if (new_dirp_l) unlock_vnode(new_dirp_l);
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if (newvmp) unlock_vmnt(newvmp);
put_vnode(old_dirp);
put_vnode(new_dirp);
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return(r);
}
/*===========================================================================*
* do_truncate *
*===========================================================================*/
int do_truncate(void)
{
/* truncate_vnode() does the actual work of do_truncate() and do_ftruncate().
* do_truncate() and do_ftruncate() have to get hold of the inode, either
* by name or fd, do checks on it, and call truncate_inode() to do the
* work.
*/
struct vnode *vp;
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struct vmnt *vmp;
int r;
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char fullpath[PATH_MAX];
struct lookup resolve;
off_t length;
vir_bytes vname;
size_t vname_length;
vname = job_m_in.m_lc_vfs_truncate.name;
vname_length = job_m_in.m_lc_vfs_truncate.len;
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lookup_init(&resolve, fullpath, PATH_NOFLAGS, &vmp, &vp);
resolve.l_vmnt_lock = VMNT_READ;
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resolve.l_vnode_lock = VNODE_WRITE;
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length = job_m_in.m_lc_vfs_truncate.offset;
if (length < 0) return(EINVAL);
/* Temporarily open file */
if (fetch_name(vname, vname_length, fullpath) != OK) return(err_code);
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if ((vp = eat_path(&resolve, fp)) == NULL) return(err_code);
/* Ask FS to truncate the file */
if ((r = forbidden(fp, vp, W_BIT)) == OK) {
/* If the file size does not change, do not make the actual call. This
* ensures that the file times are retained when the file size remains
* the same, which is a POSIX requirement.
*/
if (S_ISREG(vp->v_mode) && vp->v_size == length)
r = OK;
else
r = truncate_vnode(vp, length);
}
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unlock_vnode(vp);
unlock_vmnt(vmp);
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put_vnode(vp);
return(r);
}
/*===========================================================================*
* do_ftruncate *
*===========================================================================*/
int do_ftruncate(void)
{
/* As with do_truncate(), truncate_vnode() does the actual work. */
struct filp *rfilp;
struct vnode *vp;
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int r;
off_t length;
scratch(fp).file.fd_nr = job_m_in.m_lc_vfs_truncate.fd;
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length = job_m_in.m_lc_vfs_truncate.offset;
if (length < 0) return(EINVAL);
/* File is already opened; get a vnode pointer from filp */
if ((rfilp = get_filp(scratch(fp).file.fd_nr, VNODE_WRITE)) == NULL)
return(err_code);
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vp = rfilp->filp_vno;
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if (!(rfilp->filp_mode & W_BIT))
r = EBADF;
else if (S_ISREG(vp->v_mode) && vp->v_size == length)
/* If the file size does not change, do not make the actual call. This
* ensures that the file times are retained when the file size remains
* the same, which is a POSIX requirement.
*/
r = OK;
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else
r = truncate_vnode(vp, length);
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unlock_filp(rfilp);
return(r);
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}
/*===========================================================================*
* truncate_vnode *
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*===========================================================================*/
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int truncate_vnode(vp, newsize)
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struct vnode *vp;
off_t newsize;
{
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/* Truncate a regular file or a pipe */
int r;
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assert(tll_locked_by_me(&vp->v_lock));
if (!S_ISREG(vp->v_mode) && !S_ISFIFO(vp->v_mode)) return(EINVAL);
/* We must not compare the old and the new size here: this function may be
* called for open(2), which requires an update to the file times if O_TRUNC
* is given, even if the file size remains the same.
*/
if ((r = req_ftrunc(vp->v_fs_e, vp->v_inode_nr, newsize, 0)) == OK)
vp->v_size = newsize;
return(r);
}
/*===========================================================================*
* do_slink *
*===========================================================================*/
int do_slink(void)
{
/* Perform the symlink(name1, name2) system call. */
int r;
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struct vnode *vp;
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struct vmnt *vmp;
char fullpath[PATH_MAX];
struct lookup resolve;
vir_bytes vname1, vname2;
size_t vname1_length, vname2_length;
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lookup_init(&resolve, fullpath, PATH_NOFLAGS, &vmp, &vp);
resolve.l_vmnt_lock = VMNT_WRITE;
resolve.l_vnode_lock = VNODE_WRITE;
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vname1 = job_m_in.m_lc_vfs_link.name1;
vname1_length = job_m_in.m_lc_vfs_link.len1;
vname2 = job_m_in.m_lc_vfs_link.name2;
vname2_length = job_m_in.m_lc_vfs_link.len2;
if (vname1_length <= 1) return(ENOENT);
if (vname1_length >= _POSIX_SYMLINK_MAX) return(ENAMETOOLONG);
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/* Get dir inode of 'name2' */
if (fetch_name(vname2, vname2_length, fullpath) != OK) return(err_code);
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if ((vp = last_dir(&resolve, fp)) == NULL) return(err_code);
if ((r = forbidden(fp, vp, W_BIT|X_BIT)) == OK) {
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r = req_slink(vp->v_fs_e, vp->v_inode_nr, fullpath, who_e,
vname1, vname1_length - 1, fp->fp_effuid,
fp->fp_effgid);
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}
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unlock_vnode(vp);
unlock_vmnt(vmp);
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put_vnode(vp);
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return(r);
}
/*===========================================================================*
* rdlink_direct *
*===========================================================================*/
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int rdlink_direct(orig_path, link_path, rfp)
char *orig_path;
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char link_path[PATH_MAX]; /* should have length PATH_MAX */
struct fproc *rfp;
{
/* Perform a readlink()-like call from within the VFS */
int r;
struct vnode *vp;
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struct vmnt *vmp;
struct lookup resolve;
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lookup_init(&resolve, link_path, PATH_RET_SYMLINK, &vmp, &vp);
resolve.l_vmnt_lock = VMNT_READ;
resolve.l_vnode_lock = VNODE_READ;
/* Temporarily open the file containing the symbolic link. Use link_path
* for temporary storage to keep orig_path untouched. */
strncpy(link_path, orig_path, PATH_MAX); /* PATH_MAX includes '\0' */
link_path[PATH_MAX - 1] = '\0';
if ((vp = eat_path(&resolve, rfp)) == NULL) return(err_code);
/* Make sure this is a symbolic link */
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if (!S_ISLNK(vp->v_mode))
r = EINVAL;
else
r = req_rdlink(vp->v_fs_e, vp->v_inode_nr, NONE, (vir_bytes) link_path,
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PATH_MAX - 1, 1);
if (r > 0) link_path[r] = '\0'; /* Terminate string when succesful */
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unlock_vnode(vp);
unlock_vmnt(vmp);
put_vnode(vp);
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return r;
}
/*===========================================================================*
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* do_rdlink *
*===========================================================================*/
int do_rdlink(void)
{
/* Perform the readlink(name, buf, bufsize) system call. */
int r;
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struct vnode *vp;
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struct vmnt *vmp;
char fullpath[PATH_MAX];
struct lookup resolve;
vir_bytes vname;
size_t vname_length, buf_size;
vir_bytes buf;
vname = job_m_in.m_lc_vfs_readlink.name;
vname_length = job_m_in.m_lc_vfs_readlink.namelen;
buf = job_m_in.m_lc_vfs_readlink.buf;
buf_size = job_m_in.m_lc_vfs_readlink.bufsize;
if (buf_size > SSIZE_MAX) return(EINVAL);
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lookup_init(&resolve, fullpath, PATH_RET_SYMLINK, &vmp, &vp);
resolve.l_vmnt_lock = VMNT_READ;
resolve.l_vnode_lock = VNODE_READ;
/* Temporarily open the file containing the symbolic link */
if (fetch_name(vname, vname_length, fullpath) != OK) return(err_code);
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if ((vp = eat_path(&resolve, fp)) == NULL) return(err_code);
/* Make sure this is a symbolic link */
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if (!S_ISLNK(vp->v_mode))
r = EINVAL;
else
r = req_rdlink(vp->v_fs_e, vp->v_inode_nr, who_e, buf, buf_size, 0);
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unlock_vnode(vp);
unlock_vmnt(vmp);
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put_vnode(vp);
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return(r);
}