[PATCH AUTOSEL 5.4 5/7] wifi: ath6kl: remove WARN on bad firmware input

[Sasha Levin <sashal@kernel.org>]

From: Johannes Berg <johannes.berg@intel.com>

[ Upstream commit e7417421d89358da071fd2930f91e67c7128fbff ]

If the firmware gives bad input, that's nothing to do with
the driver's stack at this point etc., so the WARN_ON()
doesn't add any value. Additionally, this is one of the
top syzbot reports now. Just print a message, and as an
added bonus, print the sizes too.

Reported-by: syzbot+92c6dd14aaa230be6855@syzkaller.appspotmail.com
Tested-by: syzbot+92c6dd14aaa230be6855@syzkaller.appspotmail.com
Acked-by: Jeff Johnson <jeff.johnson@oss.qualcomm.com>
Link: https://patch.msgid.link/20250617114529.031a677a348e.I58bf1eb4ac16a82c546725ff010f3f0d2b0cca49@changeid
Signed-off-by: Johannes Berg <johannes.berg@intel.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---

**YES**

This commit should be backported to stable kernel trees for the
following reasons:

## Security and Stability Impact

1. **Syzbot Report**: The commit explicitly mentions this is "one of the
   top syzbot reports now", indicating it's a frequently triggered issue
   that impacts kernel stability testing. Syzbot is Google's continuous
   fuzzing infrastructure that finds kernel bugs, and high-frequency
   reports indicate significant impact.

2. **WARN_ON Misuse**: The removed WARN_ON is checking for bad firmware
   input, which violates kernel best practices. WARN_ON should only be
   used for "impossible" conditions that indicate kernel bugs, not for
   validating external input. As the commit message states: "If the
   firmware gives bad input, that's nothing to do with the driver's
   stack at this point."

3. **DoS Potential**: A WARN_ON can be triggered by malicious or
   corrupted firmware, potentially causing:
   - Stack traces in kernel logs (log spam)
   - Performance degradation
   - In some configurations, system panic (if panic_on_warn is set)

## Code Analysis

The change is minimal and safe:
```c
- WARN_ON(1);
+ ath6kl_err("mismatched byte count %d vs. expected %zd\n",
+            le32_to_cpu(targ_info->byte_count),
+            sizeof(*targ_info));
```

The fix:
- Removes the inappropriate WARN_ON
- Adds informative error logging with actual vs expected sizes
- Maintains the same error handling path (return -EINVAL)
- No functional changes beyond logging

## Similar Precedent

Looking at similar commits:
- Commit #5 (ath6kl: reduce WARN to dev_dbg() in callback) -
  **Backported: YES** - Similar removal of WARN for known race condition
- Commit #3 (ath10k: Change the warning message string) - **Backported:
  YES** - Modified warning to avoid syzbot confusion

## Stable Kernel Criteria

This meets stable kernel criteria:
- **Fixes a real bug**: Addresses inappropriate WARN_ON usage that can
  be triggered by external input
- **Minimal change**: Only removes WARN_ON and adds error message
- **Low risk**: No functional changes, just logging improvement
- **Tested**: Explicitly tested by syzbot
- **Clear benefit**: Reduces false positive warnings and improves
  debugging

The commit is a straightforward fix that improves kernel robustness
without introducing new risks, making it an ideal candidate for stable
backporting.

 drivers/net/wireless/ath/ath6kl/bmi.c | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/drivers/net/wireless/ath/ath6kl/bmi.c b/drivers/net/wireless/ath/ath6kl/bmi.c
index af98e871199d3..5a9e93fd1ef42 100644
--- a/drivers/net/wireless/ath/ath6kl/bmi.c
+++ b/drivers/net/wireless/ath/ath6kl/bmi.c
@@ -87,7 +87,9 @@ int ath6kl_bmi_get_target_info(struct ath6kl *ar,
 		 * We need to do some backwards compatibility to make this work.
 		 */
 		if (le32_to_cpu(targ_info->byte_count) != sizeof(*targ_info)) {
-			WARN_ON(1);
+			ath6kl_err("mismatched byte count %d vs. expected %zd\n",
+				   le32_to_cpu(targ_info->byte_count),
+				   sizeof(*targ_info));
 			return -EINVAL;
 		}
 
-- 
2.39.5