[PATCH 6.18 231/396] binfmt_misc: restore write access when removing an entry

6.18-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Christian Brauner <[email protected]>

commit db1856ea9196cf6e015d12199a34c0b9313c7bfa upstream.

Registering an entry with the MISC_FMT_OPEN_FILE flag opens the
interpreter via open_exec() which denies write access to it for as
long as the entry exists. Removing the entry closes the interpreter
file via filp_close() but never restores write access, leaving the
inode's i_writecount permanently negative. Opening the interpreter
for writing keeps failing with ETXTBSY long after the entry is gone
until the inode is evicted from the inode cache.

Commit 90f601b497d7 ("binfmt_misc: restore write access before
closing files opened by open_exec()") fixed the same imbalance in the
error path of bm_register_write() but the actual removal path has
been leaking the write denial since the introduction of the flag.

Restore write access in put_binfmt_handler() before closing the
interpreter file.

Link: https://patch.msgid.link/[email protected]
Fixes: 948b701a607f ("binfmt_misc: add persistent opened binary handler for containers")
Cc: [email protected]
Signed-off-by: Christian Brauner (Amutable) <[email protected]>
Signed-off-by: Greg Kroah-Hartman <[email protected]>
---
 fs/binfmt_misc.c |    4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

--- a/fs/binfmt_misc.c
+++ b/fs/binfmt_misc.c
@@ -161,8 +161,10 @@ static Node *get_binfmt_handler(struct b
 static void put_binfmt_handler(Node *e)
 {
 	if (refcount_dec_and_test(&e->users)) {
-		if (e->flags & MISC_FMT_OPEN_FILE)
+		if (e->flags & MISC_FMT_OPEN_FILE) {
+			exe_file_allow_write_access(e->interp_file);
 			filp_close(e->interp_file, NULL);
+		}
 		kfree(e);
 	}
 }