* [PATCH AUTOSEL 6.6 5/6] ksmbd: fix potential use-after-free in oplock/lease break ack
[not found] <20250714230744.3710270-1-sashal@kernel.org>
@ 2025-07-14 23:07 ` Sasha Levin
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From: Sasha Levin @ 2025-07-14 23:07 UTC (permalink / raw)
To: patches, stable
Cc: Namjae Jeon, Ziyan Xu, Steve French, Sasha Levin, smfrench,
linux-cifs
From: Namjae Jeon <linkinjeon@kernel.org>
[ Upstream commit 50f930db22365738d9387c974416f38a06e8057e ]
If ksmbd_iov_pin_rsp return error, use-after-free can happen by
accessing opinfo->state and opinfo_put and ksmbd_fd_put could
called twice.
Reported-by: Ziyan Xu <research@securitygossip.com>
Signed-off-by: Namjae Jeon <linkinjeon@kernel.org>
Signed-off-by: Steve French <stfrench@microsoft.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
LLM Generated explanations, may be completely bogus:
**YES**
This commit should be backported to stable kernel trees. Here's my
extensive analysis:
## Security Impact Analysis
This commit fixes a critical **use-after-free vulnerability** in the
oplock/lease break acknowledgment handling code paths in ksmbd (kernel
SMB server). This is a serious security issue that can lead to:
1. **Memory corruption** - Accessing freed memory can corrupt kernel
memory
2. **Kernel crashes** - Dereferencing freed pointers can cause kernel
panics
3. **Potential privilege escalation** - UAF vulnerabilities can
potentially be exploited for privilege escalation
## Code Analysis
The commit addresses a race condition where:
1. **Double-free issue**: Both `opinfo_put()` and `ksmbd_fd_put()` could
be called twice on error paths
2. **Use-after-free of opinfo->op_state**: The code was accessing
`opinfo->op_state` after potentially freeing the opinfo structure
### Specific Code Changes
In both `smb20_oplock_break_ack()` and `smb21_lease_break_ack()`, the
fix reorganizes the cleanup logic:
**Before (vulnerable pattern):**
```c
opinfo->op_state = OPLOCK_STATE_NONE;
wake_up_interruptible_all(&opinfo->oplock_q);
opinfo_put(opinfo);
ksmbd_fd_put(work, fp);
// ... response setup ...
ret = ksmbd_iov_pin_rsp(work, rsp, sizeof(...));
if (!ret)
return;
err_out:
opinfo->op_state = OPLOCK_STATE_NONE; // UAF: opinfo may be freed
wake_up_interruptible_all(&opinfo->oplock_q);
opinfo_put(opinfo); // Double-free
ksmbd_fd_put(work, fp); // Double-free
```
**After (fixed pattern):**
```c
// ... response setup ...
ret = ksmbd_iov_pin_rsp(work, rsp, sizeof(...));
if (ret) {
err_out:
smb2_set_err_rsp(work);
}
// Single cleanup path
opinfo->op_state = OPLOCK_STATE_NONE;
wake_up_interruptible_all(&opinfo->oplock_q);
opinfo_put(opinfo);
ksmbd_fd_put(work, fp);
```
## Stable Kernel Criteria
This commit meets all the stable kernel requirements:
1. **Fixes a real bug**: UAF vulnerabilities are serious security bugs
2. **Small and contained**: The fix is minimal, only reorganizing
cleanup logic
3. **No new features**: Only fixes the bug, no functional changes
4. **Low regression risk**: The change is straightforward and doesn't
modify core logic
5. **Clear fix**: The commit clearly addresses the specific UAF issue
## Historical Context
Looking at similar commits in ksmbd:
- Multiple UAF fixes have been backported (e.g., commits 18b4fac5ef17,
21a4e47578d4, a1f46c99d9ea)
- All have "Cc: stable@vger.kernel.org" tags
- This follows the same pattern of fixing race conditions and UAF issues
in SMB protocol handling
## Conclusion
This commit should be backported because:
1. It fixes a critical security vulnerability (UAF)
2. The fix is minimal and low-risk
3. It follows the pattern of other ksmbd UAF fixes that were backported
4. The vulnerability was reported by a security researcher (Ziyan Xu)
5. It prevents potential kernel crashes and exploitation
The commit follows stable tree rules perfectly - it's a targeted fix for
an important bug with minimal changes and no architectural
modifications.
fs/smb/server/smb2pdu.c | 29 +++++++++--------------------
1 file changed, 9 insertions(+), 20 deletions(-)
diff --git a/fs/smb/server/smb2pdu.c b/fs/smb/server/smb2pdu.c
index 6c22240368abf..e25c2ca56461a 100644
--- a/fs/smb/server/smb2pdu.c
+++ b/fs/smb/server/smb2pdu.c
@@ -8503,11 +8503,6 @@ static void smb20_oplock_break_ack(struct ksmbd_work *work)
goto err_out;
}
- opinfo->op_state = OPLOCK_STATE_NONE;
- wake_up_interruptible_all(&opinfo->oplock_q);
- opinfo_put(opinfo);
- ksmbd_fd_put(work, fp);
-
rsp->StructureSize = cpu_to_le16(24);
rsp->OplockLevel = rsp_oplevel;
rsp->Reserved = 0;
@@ -8515,16 +8510,15 @@ static void smb20_oplock_break_ack(struct ksmbd_work *work)
rsp->VolatileFid = volatile_id;
rsp->PersistentFid = persistent_id;
ret = ksmbd_iov_pin_rsp(work, rsp, sizeof(struct smb2_oplock_break));
- if (!ret)
- return;
-
+ if (ret) {
err_out:
+ smb2_set_err_rsp(work);
+ }
+
opinfo->op_state = OPLOCK_STATE_NONE;
wake_up_interruptible_all(&opinfo->oplock_q);
-
opinfo_put(opinfo);
ksmbd_fd_put(work, fp);
- smb2_set_err_rsp(work);
}
static int check_lease_state(struct lease *lease, __le32 req_state)
@@ -8654,11 +8648,6 @@ static void smb21_lease_break_ack(struct ksmbd_work *work)
}
lease_state = lease->state;
- opinfo->op_state = OPLOCK_STATE_NONE;
- wake_up_interruptible_all(&opinfo->oplock_q);
- atomic_dec(&opinfo->breaking_cnt);
- wake_up_interruptible_all(&opinfo->oplock_brk);
- opinfo_put(opinfo);
rsp->StructureSize = cpu_to_le16(36);
rsp->Reserved = 0;
@@ -8667,16 +8656,16 @@ static void smb21_lease_break_ack(struct ksmbd_work *work)
rsp->LeaseState = lease_state;
rsp->LeaseDuration = 0;
ret = ksmbd_iov_pin_rsp(work, rsp, sizeof(struct smb2_lease_ack));
- if (!ret)
- return;
-
+ if (ret) {
err_out:
+ smb2_set_err_rsp(work);
+ }
+
+ opinfo->op_state = OPLOCK_STATE_NONE;
wake_up_interruptible_all(&opinfo->oplock_q);
atomic_dec(&opinfo->breaking_cnt);
wake_up_interruptible_all(&opinfo->oplock_brk);
-
opinfo_put(opinfo);
- smb2_set_err_rsp(work);
}
/**
--
2.39.5
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