This is a note to let you know that I've just added the patch titled nfsd: fix use-after-free due to delegation race to the 4.9-stable tree which can be found at: http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary The filename of the patch is: nfsd-fix-use-after-free-due-to-delegation-race.patch and it can be found in the queue-4.9 subdirectory. If you, or anyone else, feels it should not be added to the stable tree, please let <stable@xxxxxxxxxxxxxxx> know about it. >From 548ec0805c399c65ed66c6641be467f717833ab5 Mon Sep 17 00:00:00 2001 From: "J. Bruce Fields" <bfields@xxxxxxxxxx> Date: Mon, 29 Nov 2021 15:08:00 -0500 Subject: nfsd: fix use-after-free due to delegation race From: J. Bruce Fields <bfields@xxxxxxxxxx> commit 548ec0805c399c65ed66c6641be467f717833ab5 upstream. A delegation break could arrive as soon as we've called vfs_setlease. A delegation break runs a callback which immediately (in nfsd4_cb_recall_prepare) adds the delegation to del_recall_lru. If we then exit nfs4_set_delegation without hashing the delegation, it will be freed as soon as the callback is done with it, without ever being removed from del_recall_lru. Symptoms show up later as use-after-free or list corruption warnings, usually in the laundromat thread. I suspect aba2072f4523 "nfsd: grant read delegations to clients holding writes" made this bug easier to hit, but I looked as far back as v3.0 and it looks to me it already had the same problem. So I'm not sure where the bug was introduced; it may have been there from the beginning. Cc: stable@xxxxxxxxxxxxxxx Signed-off-by: J. Bruce Fields <bfields@xxxxxxxxxx> [Salvatore Bonaccorso: Backport for context changes to versions which do not have 20b7d86f29d3 ("nfsd: use boottime for lease expiry calculation")] Signed-off-by: Salvatore Bonaccorso <carnil@xxxxxxxxxx> Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx> --- fs/nfsd/nfs4state.c | 9 +++++++-- 1 file changed, 7 insertions(+), 2 deletions(-) --- a/fs/nfsd/nfs4state.c +++ b/fs/nfsd/nfs4state.c @@ -955,6 +955,11 @@ hash_delegation_locked(struct nfs4_deleg return 0; } +static bool delegation_hashed(struct nfs4_delegation *dp) +{ + return !(list_empty(&dp->dl_perfile)); +} + static bool unhash_delegation_locked(struct nfs4_delegation *dp) { @@ -962,7 +967,7 @@ unhash_delegation_locked(struct nfs4_del lockdep_assert_held(&state_lock); - if (list_empty(&dp->dl_perfile)) + if (!delegation_hashed(dp)) return false; dp->dl_stid.sc_type = NFS4_CLOSED_DELEG_STID; @@ -3882,7 +3887,7 @@ static void nfsd4_cb_recall_prepare(stru * queued for a lease break. Don't queue it again. */ spin_lock(&state_lock); - if (dp->dl_time == 0) { + if (delegation_hashed(dp) && dp->dl_time == 0) { dp->dl_time = get_seconds(); list_add_tail(&dp->dl_recall_lru, &nn->del_recall_lru); } Patches currently in stable-queue which might be from bfields@xxxxxxxxxx are queue-4.9/nfsd-fix-use-after-free-due-to-delegation-race.patch