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afs: Fix directory permissions check

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Doing faccessat("/afs/some/directory", 0) triggers a BUG in the permissions
check code.

Fix this by just removing the BUG section.  If no permissions are asked
for, just return okay if the file exists.

Also:

 (1) Split up the directory check so that it has separate if-statements
     rather than if-else-if (e.g. checking for MAY_EXEC shouldn't skip the
     check for MAY_READ and MAY_WRITE).

 (2) Check for MAY_CHDIR as MAY_EXEC.

Without the main fix, the following BUG may occur:

 kernel BUG at fs/afs/security.c:386!
 invalid opcode: 0000 [#1] SMP PTI
 ...
 RIP: 0010:afs_permission+0x19d/0x1a0 [kafs]
 ...
 Call Trace:
  ? inode_permission+0xbe/0x180
  ? do_faccessat+0xdc/0x270
  ? do_syscall_64+0x60/0x1f0
  ? entry_SYSCALL_64_after_hwframe+0x49/0xbe

Fixes: 00d3b7a4533e ("[AFS]: Add security support.")
Reported-by: Jonathan Billings <jsbillings@jsbillings.org>
Signed-off-by: David Howells <dhowells@redhat.com>
This commit is contained in:
David Howells 2018-05-16 21:25:46 +01:00
parent 21b9f1c7e3
commit 378831e4da
1 changed files with 3 additions and 7 deletions
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10
fs/afs/security.c
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@ -372,18 +372,14 @@ int afs_permission(struct inode *inode, int mask)
mask, access, S_ISDIR(inode->i_mode) ? "dir" : "file"); mask, access, S_ISDIR(inode->i_mode) ? "dir" : "file");
if (S_ISDIR(inode->i_mode)) { if (S_ISDIR(inode->i_mode)) {
if (mask & MAY_EXEC) { if (mask & (MAY_EXEC | MAY_READ | MAY_CHDIR)) {
if (!(access & AFS_ACE_LOOKUP)) if (!(access & AFS_ACE_LOOKUP))
goto permission_denied; goto permission_denied;
} else if (mask & MAY_READ) { }
if (!(access & AFS_ACE_LOOKUP)) if (mask & MAY_WRITE) {
goto permission_denied;
} else if (mask & MAY_WRITE) {
if (!(access & (AFS_ACE_DELETE | /* rmdir, unlink, rename from */ if (!(access & (AFS_ACE_DELETE | /* rmdir, unlink, rename from */
AFS_ACE_INSERT))) /* create, mkdir, symlink, rename to */ AFS_ACE_INSERT))) /* create, mkdir, symlink, rename to */
goto permission_denied; goto permission_denied;
} else {
BUG();
} }
} else { } else {
if (!(access & AFS_ACE_LOOKUP)) if (!(access & AFS_ACE_LOOKUP))