From: Filipe Manana fdmanana@suse.com
[ Upstream commit 3bf179e36da917c5d9bec71c714573ed1649b7c1 ]
If insert_state() state failed it returns an error pointer and we call extent_io_tree_panic() which will trigger a BUG() call. However if CONFIG_BUG is disabled, which is an uncommon and exotic scenario, then we fallthrough and call cache_state() which will dereference the error pointer, resulting in an invalid memory access.
So jump to the 'out' label after calling extent_io_tree_panic(), it also makes the code more clear besides dealing with the exotic scenario where CONFIG_BUG is disabled.
Signed-off-by: Filipe Manana fdmanana@suse.com Reviewed-by: David Sterba dsterba@suse.com Signed-off-by: David Sterba dsterba@suse.com Signed-off-by: Sasha Levin sashal@kernel.org ---
**YES** This commit should be backported to stable kernel trees. **Detailed Analysis:** **1. Bug Description and Impact:** The commit fixes a serious potential memory corruption bug in the btrfs filesystem. When `insert_state()` fails in `btrfs_convert_extent_bit()`, it returns an error pointer (ERR_PTR). The current code calls `extent_io_tree_panic()` which triggers `BUG()`, but if `CONFIG_BUG` is disabled, the code continues executing and calls `cache_state(inserted_state, cached_state)` with the error pointer, causing invalid memory access. **2. Code Changes Analysis:** The fix is minimal and surgical - just adding a single `goto out;` statement after the `extent_io_tree_panic()` call: ```c if (IS_ERR(inserted_state)) { ret = PTR_ERR(inserted_state); extent_io_tree_panic(tree, prealloc, "insert", ret); + goto out; // <-- The fix } ``` This ensures that when `CONFIG_BUG` is disabled, execution jumps to the cleanup code instead of continuing with an invalid pointer. **3. Comparison with Similar Commits:** This commit aligns with the pattern seen in "Similar Commit #2" (Status: YES), which also: - Removes reliance on `BUG_ON()` behavior - Provides graceful error handling - Has minimal risk - Fixes a potential crash/corruption scenario Similar to commit #3 and #5 (both Status: NO), this touches BUG() handling, but unlike those commits which make broader architectural changes to error handling patterns, this fix is much more contained. **4. Stable Tree Criteria Assessment:** ✅ **Fixes important bug**: Prevents potential memory corruption/crashes ✅ **Small and contained**: Single line addition ✅ **Minimal risk**: Only affects error path when insert_state() fails AND CONFIG_BUG is disabled ✅ **No new features**: Pure bug fix ✅ **No architectural changes**: Preserves existing error handling, just prevents fallthrough ✅ **Critical subsystem**: btrfs filesystem corruption prevention ✅ **Clear side effects**: No unintended consequences beyond fixing the bug **5. Risk Assessment:** - **Very Low Risk**: The change only affects an error condition that's already problematic - **Exotic scenario**: Only impacts systems with `CONFIG_BUG` disabled (uncommon but not impossible) - **No regression potential**: The change only prevents executing invalid code, doesn't change normal operation - **Well-contained**: Affects only one function in one file **6. Security Implications:** While `CONFIG_BUG` disabled is uncommon, this could potentially be exploited if an attacker can trigger the `insert_state()` failure condition, leading to memory corruption. The fix prevents this attack vector. This is a clear candidate for stable backporting - it fixes a real bug with minimal risk and follows the stable tree rules perfectly.
fs/btrfs/extent-io-tree.c | 1 + 1 file changed, 1 insertion(+)
diff --git a/fs/btrfs/extent-io-tree.c b/fs/btrfs/extent-io-tree.c index 13de6af279e52..92cfde37b1d33 100644 --- a/fs/btrfs/extent-io-tree.c +++ b/fs/btrfs/extent-io-tree.c @@ -1456,6 +1456,7 @@ int convert_extent_bit(struct extent_io_tree *tree, u64 start, u64 end, if (IS_ERR(inserted_state)) { ret = PTR_ERR(inserted_state); extent_io_tree_panic(tree, prealloc, "insert", ret); + goto out; } cache_state(inserted_state, cached_state); if (inserted_state == prealloc)