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Allow make-* flags with remount operations

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While the mount syscall documentation disallows this, the kernel silently
ignores make-* flags when doing a remount, and real applications were
passing this conflicting set of flags. Because changing the kernel to
reject this combination would break userspace, we should allow them
instead.

For an example: see https://bugs.launchpad.net/apparmor/+bug/2091424.

Signed-off-by: Ryan Lee <ryan.lee@canonical.com>
This commit is contained in:
Ryan Lee 2024-12-17 11:59:54 -08:00
parent 6d7b5df947
commit 52babe8054
1 changed files with 7 additions and 1 deletions
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8
parser/mount.h
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@ -108,7 +108,13 @@
#define MS_MOVE_FLAGS (MS_MOVE) #define MS_MOVE_FLAGS (MS_MOVE)
#define MS_CMDS (MS_MOVE | MS_REMOUNT | MS_BIND | MS_RBIND | MS_MAKE_CMDS) #define MS_CMDS (MS_MOVE | MS_REMOUNT | MS_BIND | MS_RBIND | MS_MAKE_CMDS)
#define MS_REMOUNT_FLAGS (MS_ALL_FLAGS & ~(MS_CMDS & ~MS_REMOUNT & ~MS_BIND & ~MS_RBIND)) /*
* This allows MS_MAKE_CMDS, by design: while remount and make-* shouldn't be
* used together, real-world applications do use them together, and the Linux
* kernel ignores the make-* flags when doing a remount instead of returning
* EINVAL. See https://bugs.launchpad.net/apparmor/+bug/2091424 for an example.
*/
#define MS_REMOUNT_FLAGS (MS_ALL_FLAGS & ~MS_MOVE_FLAGS)
#define MS_NEW_FLAGS (MS_ALL_FLAGS & ~MS_CMDS) #define MS_NEW_FLAGS (MS_ALL_FLAGS & ~MS_CMDS)
#define MNT_SRC_OPT 1 #define MNT_SRC_OPT 1