Commit 378831e4 authored May 16, 2018 by David Howells

afs: Fix directory permissions check



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: 00d3b7a4 ("[AFS]: Add security support.")
Reported-by: Jonathan Billings <jsbillings@jsbillings.org>
Signed-off-by: David Howells <dhowells@redhat.com>

parent 21b9f1c7

fs/afs/security.c

+3 −7

Original line number	Diff line number	Diff line
		@@ -372,18 +372,14 @@ int afs_permission(struct inode *inode, int mask)
		mask, access, S_ISDIR(inode->i_mode) ? "dir" : "file");

		if (S_ISDIR(inode->i_mode)) {
		if (mask & MAY_EXEC) {
		if (mask & (MAY_EXEC \| MAY_READ \| MAY_CHDIR)) {
		if (!(access & AFS_ACE_LOOKUP))
		goto permission_denied;
		} else if (mask & MAY_READ) {
		if (!(access & AFS_ACE_LOOKUP))
		goto permission_denied;
		} else if (mask & MAY_WRITE) {
		}
		if (mask & MAY_WRITE) {
		if (!(access & (AFS_ACE_DELETE \| /* rmdir, unlink, rename from */
		AFS_ACE_INSERT))) /* create, mkdir, symlink, rename to */
		goto permission_denied;
		} else {
		BUG();
		}
		} else {
		if (!(access & AFS_ACE_LOOKUP))

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