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fs/vfs: enforce pseudoFS permissions on mutation operations

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Add pseudoFS permission enforcement for unlink(), mkdir(), and rename() VFS mutation operations.

This change validates parent-directory permissions before modifying pseudoFS inode topology and returns -EACCES for unauthorized operations.

The implementation preserves mountpoint filesystem behavior and fixes multiple inode lifetime/search-state issues in the rename path.

Signed-off-by: Abhishek Mishra <mishra.abhishek2808@gmail.com>
This commit is contained in:
Abhishek Mishra 2026-05-19 12:50:29 +00:00 • committed by Xiang Xiao
parent 59a66fa17d
commit fa7f85632c
5 changed files with 206 additions and 88 deletions
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193
fs/inode/fs_inode.c
View file

@ -27,6 +27,7 @@
#include <assert.h>
#include <errno.h>
#include <fcntl.h>
#include <unistd.h>
#include <nuttx/fs/fs.h>
#include <nuttx/rwsem.h>
@ -48,6 +49,70 @@
static rw_semaphore_t g_inode_lock = RWSEM_INITIALIZER;
/****************************************************************************
* Private Functions
****************************************************************************/
/****************************************************************************
* Name: _inode_checkmode
*
* Description:
* Test effective credentials against 'inode' for 'amode' access.
* Kernel threads always pass.
*
* Returned Value:
* Zero (OK) or -EACCES.
*
****************************************************************************/
#if defined(CONFIG_PSEUDOFS_ATTRIBUTES) && defined(CONFIG_SCHED_USER_IDENTITY)
static int _inode_checkmode(FAR struct inode *inode, int amode)
{
FAR struct tcb_s *rtcb;
mode_t perm;
uid_t uid;
gid_t gid;
/* Kernel threads are always granted access */
rtcb = nxsched_self();
if ((rtcb->flags & TCB_FLAG_TTYPE_MASK) == TCB_FLAG_TTYPE_KERNEL)
{
return OK;
}
/* Use effective credentials */
DEBUGASSERT(rtcb->group != NULL);
uid = rtcb->group->tg_euid;
gid = rtcb->group->tg_egid;
/* Select the applicable permission-bit triplet */
if (uid == inode->i_owner)
{
perm = (inode->i_mode >> 6) & 7;
}
else if (gid == inode->i_group)
{
perm = (inode->i_mode >> 3) & 7;
}
else
{
perm = inode->i_mode & 7;
}
/* Every requested bit must be present in the selected triplet */
if ((amode & perm) != amode)
{
return -EACCES;
}
return OK;
}
#endif /* CONFIG_PSEUDOFS_ATTRIBUTES && CONFIG_SCHED_USER_IDENTITY */
/****************************************************************************
* Public Functions
****************************************************************************/
@ -124,49 +189,45 @@ void inode_runlock(void)
* Name: inode_checkperm
*
* Description:
* Validate that 'inode' can be opened with the access described by
* 'oflags'. Two sequential checks are performed:
*
* 1. Operation-support check (all inode types, unconditional):
* Verifies the driver exposes the read/write entry points required by
* 'oflags'. Returns -ENXIO when ops are NULL and -EACCES when the
* required entry point is absent. Pseudo-directory inodes
* (INODE_IS_PSEUDODIR) are exempted from this step.
*
* 2. UNIX permission check (pseudo-filesystem inodes only):
* Compares effective uid/gid against i_mode owner/group/other bits.
* Mountpoint inodes and kernel threads are unconditionally exempted.
* Requires CONFIG_PSEUDOFS_ATTRIBUTES and CONFIG_SCHED_USER_IDENTITY;
* when either option is disabled this step is a no-op.
* Validate open access to 'inode' for 'oflags'. Checks driver operation
* support, then pseudo-filesystem mode bits when enabled. Mountpoints
* are exempt from mode checks.
*
* Input Parameters:
* inode - The inode to check
* oflags - Open flags (O_RDONLY / O_WRONLY / O_RDWR)
*
* Returned Value:
* Zero (OK) on success. Negated errno on failure:
* -ENXIO ops pointer is NULL
* -EACCES required operation not supported, or permission denied
* Zero (OK) on success, or a negated errno on failure.
*
****************************************************************************/
int inode_checkperm(FAR struct inode *inode, int oflags)
{
#if defined(CONFIG_PSEUDOFS_ATTRIBUTES) && defined(CONFIG_SCHED_USER_IDENTITY)
FAR struct tcb_s *rtcb;
mode_t perm;
uid_t uid;
gid_t gid;
int amode = 0;
#endif
FAR const struct file_operations *ops;
/* === Step 1: operation-support check === */
#if defined(CONFIG_PSEUDOFS_ATTRIBUTES) && defined(CONFIG_SCHED_USER_IDENTITY)
if ((oflags & O_RDOK) != 0)
{
amode |= R_OK;
}
/* Pseudo-directories carry no ops and are always accessible */
if ((oflags & O_WROK) != 0)
{
amode |= W_OK;
}
#endif
if (INODE_IS_PSEUDODIR(inode))
{
#if defined(CONFIG_PSEUDOFS_ATTRIBUTES) && defined(CONFIG_SCHED_USER_IDENTITY)
return _inode_checkmode(inode, amode);
#else
return OK;
#endif
}
ops = inode->u.i_ops;
@ -185,61 +246,51 @@ int inode_checkperm(FAR struct inode *inode, int oflags)
#if defined(CONFIG_PSEUDOFS_ATTRIBUTES) && defined(CONFIG_SCHED_USER_IDENTITY)
/* === Step 2: UNIX permission check (pseudo-filesystem inodes only) === */
/* Mountpoints delegate permission enforcement to the underlying
* filesystem
*/
if (INODE_IS_MOUNTPT(inode))
{
return OK;
}
/* Kernel threads are always granted access */
rtcb = nxsched_self();
if ((rtcb->flags & TCB_FLAG_TTYPE_MASK) == TCB_FLAG_TTYPE_KERNEL)
{
return OK;
}
/* Use effective credentials */
DEBUGASSERT(rtcb->group != NULL);
uid = rtcb->group->tg_euid;
gid = rtcb->group->tg_egid;
/* Select the applicable permission-bit triplet */
if (uid == inode->i_owner)
{
perm = (inode->i_mode >> 6) & 7;
}
else if (gid == inode->i_group)
{
perm = (inode->i_mode >> 3) & 7;
}
else
{
perm = inode->i_mode & 7;
}
/* Bit 2 (value 4) = read permission */
if (((oflags & O_RDOK) != 0) && ((perm & 4) == 0))
{
return -EACCES;
}
/* Bit 1 (value 2) = write permission */
if (((oflags & O_WROK) != 0) && ((perm & 2) == 0))
{
return -EACCES;
}
return _inode_checkmode(inode, amode);
#endif /* CONFIG_PSEUDOFS_ATTRIBUTES && CONFIG_SCHED_USER_IDENTITY */
return OK;
}
/****************************************************************************
* Name: inode_checkdirperm
*
* Description:
* Check parent directory 'dir' for 'amode' access on pseudo-filesystem
* inodes. NULL 'dir' (root) and mountpoints are exempt.
*
* Input Parameters:
* dir - Parent directory inode, or NULL for a root-level path
* amode - Access mode bitmask (R_OK / W_OK / X_OK)
*
* Returned Value:
* Zero (OK) on success, or -EACCES if permission is denied.
*
****************************************************************************/
int inode_checkdirperm(FAR struct inode *dir, int amode)
{
#if defined(CONFIG_PSEUDOFS_ATTRIBUTES) && defined(CONFIG_SCHED_USER_IDENTITY)
if (dir == NULL)
{
return OK;
}
if (INODE_IS_MOUNTPT(dir))
{
return OK;
}
return _inode_checkmode(dir, amode);
#else
return OK;
#endif /* CONFIG_PSEUDOFS_ATTRIBUTES && CONFIG_SCHED_USER_IDENTITY */
}

37
fs/inode/inode.h
View file

@ -422,32 +422,39 @@ void inode_release(FAR struct inode *inode);
* Name: inode_checkperm
*
* Description:
* Validate that 'inode' can be opened with the access described by
* 'oflags'. Two sequential checks are performed:
*
* 1. Operation-support check (all inode types):
* Ensures the driver exposes the read/write entry points required by
* 'oflags'. Pseudo-directory inodes are exempted.
*
* 2. UNIX permission check (pseudo-filesystem inodes only):
* Compares effective uid/gid against i_mode owner/group/other bits.
* Mountpoint inodes and kernel threads are unconditionally exempted.
* Active only when CONFIG_PSEUDOFS_ATTRIBUTES and
* CONFIG_SCHED_USER_IDENTITY are both enabled.
* Validate open access to 'inode' for 'oflags'. Checks driver operation
* support, then pseudo-filesystem mode bits when enabled. Mountpoints
* are exempt from mode checks.
*
* Input Parameters:
* inode - The inode to check
* oflags - Open flags (O_RDONLY / O_WRONLY / O_RDWR)
*
* Returned Value:
* Zero (OK) on success. Negated errno on failure:
* -ENXIO ops pointer is NULL
* -EACCES required operation not supported, or permission denied
* Zero (OK) on success, or a negated errno on failure.
*
****************************************************************************/
int inode_checkperm(FAR struct inode *inode, int oflags);
/****************************************************************************
* Name: inode_checkdirperm
*
* Description:
* Check parent directory 'dir' for 'amode' access on pseudo-filesystem
* inodes. NULL 'dir' (root) and mountpoints are exempt.
*
* Input Parameters:
* dir - Parent directory inode, or NULL for a root-level path
* amode - Access mode bitmask (R_OK / W_OK / X_OK)
*
* Returned Value:
* Zero (OK) on success, or -EACCES if permission is denied.
*
****************************************************************************/
int inode_checkdirperm(FAR struct inode *dir, int amode);
/****************************************************************************
* Name: foreach_inode
*

13
fs/vfs/fs_mkdir.c
View file

@ -31,6 +31,7 @@
#include <stdbool.h>
#include <assert.h>
#include <errno.h>
#include <unistd.h>
#include <nuttx/fs/fs.h>
@ -136,6 +137,18 @@ int mkdir(const char *pathname, mode_t mode)
else
{
/* Verify write+search permission on the parent directory before
* adding a new name to the pseudo-filesystem tree. POSIX requires
* both W_OK and X_OK to create a directory entry.
*/
ret = inode_checkdirperm(desc.parent, W_OK | X_OK);
if (ret < 0)
{
errcode = -ret;
goto errout_with_search;
}
/* Create an inode in the pseudo-filesystem at this path.
* NOTE that the new inode will be created with a reference
* count of zero.

43
fs/vfs/fs_rename.c
View file

@ -33,6 +33,7 @@
#include <libgen.h>
#include <assert.h>
#include <errno.h>
#include <unistd.h>
#include <nuttx/fs/fs.h>
#include <nuttx/lib/lib.h>
@ -66,21 +67,35 @@
#ifndef CONFIG_DISABLE_PSEUDOFS_OPERATIONS
static int pseudorename(FAR const char *oldpath, FAR struct inode *oldinode,
FAR struct inode *oldparent,
FAR const char *newpath)
{
struct inode_search_s newdesc;
struct inode_search_s pardesc;
FAR struct inode *newinode;
FAR struct inode *parnode;
FAR char *subdir = NULL;
#ifdef CONFIG_FS_NOTIFY
bool isdir = INODE_IS_PSEUDODIR(oldinode);
#endif
int ret;
/* SETUP_SEARCH early so RELEASE_SEARCH at errout is safe. */
SETUP_SEARCH(&newdesc, newpath, true);
/* Verify source parent write permission. */
ret = inode_checkdirperm(oldparent, W_OK);
if (ret < 0)
{
goto errout;
}
/* According to POSIX, any new inode at this path should be removed
* first, provided that it is not a directory.
*/
SETUP_SEARCH(&newdesc, newpath, true);
ret = inode_find(&newdesc);
if (ret >= 0)
{
@ -156,6 +171,30 @@ static int pseudorename(FAR const char *oldpath, FAR struct inode *oldinode,
inode_release(newinode);
}
/* Re-resolve the final destination parent after path rewrite. */
SETUP_SEARCH(&pardesc, newpath, true);
inode_find(&pardesc); /* pardesc.parent valid even if node not found */
parnode = pardesc.node;
ret = inode_checkdirperm(pardesc.parent, W_OK);
/* inode_find() holds a reference on parnode; RELEASE_SEARCH() only
* frees pardesc.buffer.
*/
if (parnode != NULL)
{
inode_release(parnode);
}
RELEASE_SEARCH(&pardesc);
if (ret < 0)
{
goto errout;
}
/* Create a new, empty inode at the destination location.
* NOTE that the new inode will be created with a reference count
* of zero.
@ -505,7 +544,7 @@ int rename(FAR const char *oldpath, FAR const char *newpath)
#endif /* CONFIG_DISABLE_MOUNTPOINT */
#ifndef CONFIG_DISABLE_PSEUDOFS_OPERATIONS
{
ret = pseudorename(oldpath, oldinode, newpath);
ret = pseudorename(oldpath, oldinode, olddesc.parent, newpath);
}
#else
{

8
fs/vfs/fs_unlink.c
View file

@ -121,6 +121,14 @@ int nx_unlink(FAR const char *pathname)
goto errout_with_inode;
}
/* Verify parent-directory write permission before unlink. */
ret = inode_checkdirperm(desc.parent, W_OK);
if (ret < 0)
{
goto errout_with_inode;
}
/* Notify the driver that it has been unlinked. If there are no
* open references to the driver instance, then the driver should
* release all resources because it is no longer accessible.