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nfsd: release path refs on follow_down() error

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nfsd_cross_mnt() initializes a local struct path with mntget() and
dget() before calling follow_down(). On a negative return the error
arm jumps to out without releasing those references:

    err = follow_down(&path, follow_flags);
    if (err < 0)
            goto out;

follow_down() never drops the caller's entry-time refs on any error
sub-case; for example a pre-cross d_manage() failure leaves path
untouched, so the mntget()/dget() taken on entry survive the call.

Every other early-exit arm in nfsd_cross_mnt() (other-namespace
return, IS_ERR(exp2), and the success tail after the swap) already
calls path_put(&path); the err < 0 arm is the lone omission. The
leak inflates mnt_count and d_count on each failed cross-mount,
blocking umount and pinning dentries against the shrinker, and is
reachable by any authenticated NFS client through nfsd_lookup_dentry
or the NFSv4 READDIR encode path.

Fix by calling path_put(&path) before the goto out in the err < 0
arm so the entry-time refs are released on all follow_down() error
returns.

Fixes: cc53ce53c8 ("Add a dentry op to allow processes to be held during pathwalk transit")
Cc: stable@vger.kernel.org
Assisted-by: kres:claude-opus-4-7
Signed-off-by: Chris Mason <clm@meta.com>
Link: https://patch.msgid.link/20260531-nfsd-testing-v1-2-7bfa481b0540@kernel.org
Signed-off-by: Chuck Lever <chuck.lever@oracle.com>
This commit is contained in:
Chris Mason
2026-05-31 08:06:59 -04:00
committed by Chuck Lever
parent 71d0684900
commit 6cba08dc19
1 changed files with 3 additions and 1 deletions
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4
fs/nfsd/vfs.c
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@@ -137,8 +137,10 @@ nfsd_cross_mnt(struct svc_rqst *rqstp, struct dentry **dpp,
follow_flags = LOOKUP_AUTOMOUNT;
err = follow_down(&path, follow_flags);
if (err < 0)
if (err < 0) {
path_put(&path);
goto out;
}
if (path.mnt == exp->ex_path.mnt && path.dentry == dentry &&
nfsd_mountpoint(dentry, exp) == 2) {
/* This is only a mountpoint in some other namespace */