FAILED: patch "[PATCH] libceph: fix two unsafe bare decodes in decode_lockers()" failed to apply to 5.15-stable tree

The patch below does not apply to the 5.15-stable tree.
If someone wants it applied there, or to any other stable or longterm tree, then please email the backport, including the original git commit id to <[email protected]>.

To reproduce the conflict and resubmit, you may use the following commands:

git fetch https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/ linux-5.15.y
git checkout FETCH_HEAD
git cherry-pick -x a109a556115271ca7896dcda7b4b7e45e156c227
# <resolve conflicts, build, test, etc.>
git commit -s
git send-email --to '<[email protected]>' --in-reply-to '2026072948-stoplight-alike-d460@gregkh' --subject-prefix 'PATCH 5.15.y' 'HEAD^..'

Possible dependencies:

thanks,

greg k-h

------------------ original commit in Linus's tree ------------------

From a109a556115271ca7896dcda7b4b7e45e156c227 Mon Sep 17 00:00:00 2001
From: Pavitra Jha <[email protected]>
Date: Tue, 2 Jun 2026 00:17:35 -0400
Subject: [PATCH] libceph: fix two unsafe bare decodes in decode_lockers()

decode_lockers() in cls_lock_client.c contains two bare decode operations that allow a malicious or compromised OSD to trigger slab-out-of-bounds reads:

1. ceph_decode_32(p) at the num_lockers field has no preceding bounds check. ceph_start_decoding() accepts struct_len=0 as valid -- the internal ceph_decode_need(p, end, 0, bad) always passes -- so when an OSD sends struct_len=0, ceph_start_decoding() returns success with p == end. The immediately following bare ceph_decode_32(p) then reads 4 bytes past the validated buffer boundary. The garbage value is passed directly to kzalloc_objs() as the locker count.

The sibling function decode_watchers() in osd_client.c already uses ceph_decode_32_safe() after its own ceph_start_decoding() call. decode_lockers() was the only site using the bare variant.

2. ceph_decode_8(p) after the decode_locker() loop has no preceding bounds check. If an OSD crafts num_lockers such that the loop advances p exactly to end, the subsequent bare ceph_decode_8(p) reads one byte past the validated buffer boundary. The result is passed directly into *type, which is used as a lock type discriminator by callers, giving an OSD-controlled one-byte OOB read with direct influence over the lock type field.

Fix both by replacing bare operations with their safe variants:
ceph_decode_32(p) -> ceph_decode_32_safe(p, end, *num_lockers,
err_inval)
ceph_decode_8(p) -> ceph_decode_8_safe(p, end, *type,
err_free_lockers)

The goto targets differ intentionally:
err_inval: is a new label returning -EINVAL directly. It is used for the pre-allocation failure path where *lockers is not yet allocated and must not be passed to ceph_free_lockers().

err_free_lockers: is the existing label. It is used for the post-allocation failure path where *lockers is allocated and must be freed.

ret is set to -EINVAL before ceph_decode_8_safe() so that err_free_lockers returns the correct error code on bounds violation. Without this, err_free_lockers would return a stale ret value (0 from the successful decode_locker() loop), silently swallowing the error.

-EINVAL is correct for both failure paths. The data received from the OSD is structurally malformed. -ENOMEM would misrepresent the failure class to callers and to stable@ backporters triaging error paths.

Attacker model: a malicious or compromised OSD in a multi-tenant Ceph deployment can trigger this against any kernel client that issues the lock.get_info class method (e.g. during RBD exclusive lock acquisition).

[ idryomov: trim changelog, formatting ]

index c6956f1df333..377336982f7d 100644
@@ -299,7 +299,7 @@ static int decode_lockers(void **p, void *end, u8 *type, char **tag,
 	if (ret)
 		return ret;
 
-	*num_lockers = ceph_decode_32(p);
+	ceph_decode_32_safe(p, end, *num_lockers, err_inval);
 	*lockers = kzalloc_objs(**lockers, *num_lockers, GFP_NOIO);
 	if (!*lockers)
 		return -ENOMEM;

@@ -310,7 +310,8 @@ static int decode_lockers(void **p, void *end, u8 *type, char **tag,
 			goto err_free_lockers;
 	}
 
-	*type = ceph_decode_8(p);
+	ret = -EINVAL;
+	ceph_decode_8_safe(p, end, *type, err_free_lockers);
 	s = ceph_extract_encoded_string(p, end, NULL, GFP_NOIO);
 	if (IS_ERR(s)) {
 		ret = PTR_ERR(s);

@@ -320,6 +321,9 @@ static int decode_lockers(void **p, void *end, u8 *type, char **tag,
 	*tag = s;
 	return 0;
 
+err_inval:
+	return -EINVAL;
+
 err_free_lockers:
 	ceph_free_lockers(*lockers, *num_lockers);
 	return ret;

From: Pavitra Jha <[email protected]>

[ Upstream commit a109a556115271ca7896dcda7b4b7e45e156c227 ]

decode_lockers() in cls_lock_client.c contains two bare decode operations that allow a malicious or compromised OSD to trigger slab-out-of-bounds reads:

1. ceph_decode_32(p) at the num_lockers field has no preceding bounds check. ceph_start_decoding() accepts struct_len=0 as valid -- the internal ceph_decode_need(p, end, 0, bad) always passes -- so when an OSD sends struct_len=0, ceph_start_decoding() returns success with p == end. The immediately following bare ceph_decode_32(p) then reads 4 bytes past the validated buffer boundary. The garbage value is passed directly to kzalloc_objs() as the locker count.

The sibling function decode_watchers() in osd_client.c already uses ceph_decode_32_safe() after its own ceph_start_decoding() call. decode_lockers() was the only site using the bare variant.

2. ceph_decode_8(p) after the decode_locker() loop has no preceding bounds check. If an OSD crafts num_lockers such that the loop advances p exactly to end, the subsequent bare ceph_decode_8(p) reads one byte past the validated buffer boundary. The result is passed directly into *type, which is used as a lock type discriminator by callers, giving an OSD-controlled one-byte OOB read with direct influence over the lock type field.

Fix both by replacing bare operations with their safe variants:
ceph_decode_32(p) -> ceph_decode_32_safe(p, end, *num_lockers,
err_inval)
ceph_decode_8(p) -> ceph_decode_8_safe(p, end, *type,
err_free_lockers)

The goto targets differ intentionally:
err_inval: is a new label returning -EINVAL directly. It is used for the pre-allocation failure path where *lockers is not yet allocated and must not be passed to ceph_free_lockers().

err_free_lockers: is the existing label. It is used for the post-allocation failure path where *lockers is allocated and must be freed.

ret is set to -EINVAL before ceph_decode_8_safe() so that err_free_lockers returns the correct error code on bounds violation. Without this, err_free_lockers would return a stale ret value (0 from the successful decode_locker() loop), silently swallowing the error.

-EINVAL is correct for both failure paths. The data received from the OSD is structurally malformed. -ENOMEM would misrepresent the failure class to callers and to stable@ backporters triaging error paths.

Attacker model: a malicious or compromised OSD in a multi-tenant Ceph deployment can trigger this against any kernel client that issues the lock.get_info class method (e.g. during RBD exclusive lock acquisition).

[ idryomov: trim changelog, formatting ]

---
 net/ceph/cls_lock_client.c | 8 ++++++--
 1 file changed, 6 insertions(+), 2 deletions(-)

index 66136a4c1ce7f..639793597b76c 100644
@@ -299,7 +299,7 @@ static int decode_lockers(void **p, void *end, u8 *type, char **tag,
 	if (ret)
 		return ret;
 
-	*num_lockers = ceph_decode_32(p);
+	ceph_decode_32_safe(p, end, *num_lockers, err_inval);
 	*lockers = kcalloc(*num_lockers, sizeof(**lockers), GFP_NOIO);
 	if (!*lockers)
 		return -ENOMEM;

@@ -310,7 +310,8 @@ static int decode_lockers(void **p, void *end, u8 *type, char **tag,
 			goto err_free_lockers;
 	}
 
-	*type = ceph_decode_8(p);
+	ret = -EINVAL;
+	ceph_decode_8_safe(p, end, *type, err_free_lockers);
 	s = ceph_extract_encoded_string(p, end, NULL, GFP_NOIO);
 	if (IS_ERR(s)) {
 		ret = PTR_ERR(s);

@@ -320,6 +321,9 @@ static int decode_lockers(void **p, void *end, u8 *type, char **tag,
 	*tag = s;
 	return 0;
 
+err_inval:
+	return -EINVAL;
+
 err_free_lockers:
 	ceph_free_lockers(*lockers, *num_lockers);
 	return ret;

2.53.0