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statx: Kill fd-with-NULL-path support in favour of AT_EMPTY_PATH

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With the new statx() syscall, the following both allow the attributes of
the file attached to a file descriptor to be retrieved:

	statx(dfd, NULL, 0, ...);

and:

	statx(dfd, "", AT_EMPTY_PATH, ...);

Change the code to reject the first option, though this means copying
the path and engaging pathwalk for the fstat() equivalent.  dfd can be a
non-directory provided path is "".

[ The timing of this isn't wonderful, but applying this now before we
  have statx() in any released kernel, before anybody starts using the
  NULL special case.    - Linus ]

Fixes: a528d35e8b ("statx: Add a system call to make enhanced file info available")
Reported-by: Michael Kerrisk <mtk.manpages@gmail.com>
Signed-off-by: David Howells <dhowells@redhat.com>
cc: Eric Sandeen <sandeen@sandeen.net>
cc: fstests@vger.kernel.org
cc: linux-api@vger.kernel.org
cc: linux-man@vger.kernel.org
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
This commit is contained in:
David Howells 2017-04-26 22:15:55 +01:00 committed by Linus Torvalds
parent fc08b197bb
commit 1e2f82d1e9
1 changed files with 6 additions and 7 deletions
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13
fs/stat.c
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@ -547,13 +547,13 @@ cp_statx(const struct kstat *stat, struct statx __user *buffer)
/**
* sys_statx - System call to get enhanced stats
* @dfd: Base directory to pathwalk from *or* fd to stat.
* @filename: File to stat *or* NULL.
* @filename: File to stat or "" with AT_EMPTY_PATH
* @flags: AT_* flags to control pathwalk.
* @mask: Parts of statx struct actually required.
* @buffer: Result buffer.
*
* Note that if filename is NULL, then it does the equivalent of fstat() using
* dfd to indicate the file of interest.
* Note that fstat() can be emulated by setting dfd to the fd of interest,
* supplying "" as the filename and setting AT_EMPTY_PATH in the flags.
*/
SYSCALL_DEFINE5(statx,
int, dfd, const char __user *, filename, unsigned, flags,
@ -567,11 +567,10 @@ SYSCALL_DEFINE5(statx,
return -EINVAL;
if ((flags & AT_STATX_SYNC_TYPE) == AT_STATX_SYNC_TYPE)
return -EINVAL;
if (!filename)
return -EINVAL;
if (filename)
error = vfs_statx(dfd, filename, flags, &stat, mask);
else
error = vfs_statx_fd(dfd, &stat, mask, flags);
error = vfs_statx(dfd, filename, flags, &stat, mask);
if (error)
return error;