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[34.87.28.213]) by smtp.gmail.com with ESMTPSA id 5a478bee46e88-30f116065c5sm13284830eec.11.2026.07.02.21.25.10 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Thu, 02 Jul 2026 21:25:13 -0700 (PDT) From: Aditya Srivastava To: Theodore Ts'o Cc: Andreas Dilger , Jan Kara , Baokun Li , Ojaswin Mujoo , Ritesh Harjani , Zhang Yi , Tao Ma , syzbot+0c89d865531d053abb2d@syzkaller.appspotmail.com, linux-ext4@vger.kernel.org, linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org, Aditya Prakash Srivastava Subject: [PATCH v3] ext4: use fsdata to track inline data write state and fix race Date: Fri, 3 Jul 2026 04:24:42 +0000 Message-ID: <20260703042443.1655-1-aditya.ansh182@gmail.com> X-Mailer: git-send-email 2.43.0 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit From: Aditya Prakash Srivastava Instead of checking the live inode state (ext4_has_inline_data(inode) and ext4_test_inode_state(inode, EXT4_STATE_MAY_INLINE_DATA)) in the write_end handlers, use the fsdata parameter of the address space operations to explicitly pass down the state in which write_begin prepared the write. A concurrent thread (such as ext4_page_mkwrite()) can convert the inline data to an extent between write_begin and write_end. If this happens, the write_end handlers would previously miss the inline write_end path and fall through to extent-based write_end logic. However, since block buffers were never allocated in write_begin, this resulted in NULL pointer dereferences or data loss because folio_buffers(folio) was NULL. Define EXT4_WRITE_DATA_INLINE (4) as a bit flag (Bit 2), treating fsdata as bitwise flags rather than mutually exclusive enums to keep states of the write path independent. Communicate this state via fsdata: 1) ext4_write_begin() and ext4_da_write_begin() set the EXT4_WRITE_DATA_INLINE bit in *fsdata via bitwise OR when an inline write is successfully prepared. 2) On entry, ext4_write_begin() clears the EXT4_WRITE_DATA_INLINE bit to safely handle VFS retries (where generic_perform_write() bypasses the fsdata initialization on its retry jump). 3) The write_end handlers perform a bitwise AND to check if the EXT4_WRITE_DATA_INLINE bit is set and invoke the inline write_end helper accordingly. Furthermore, during a buffered write, ext4_write_inline_data_end() acquires the xattr lock after preparing the write. If a concurrent page fault (ext4_page_mkwrite()) converts the inline data to an extent after the write_end handlers check the state but before ext4_write_inline_data_end() acquires the xattr write lock, the subsequent check will trigger a kernel panic via BUG_ON(!ext4_has_inline_data(inode)). To keep git history working and bisectability clean, replace the BUG_ON check in ext4_write_inline_data_end() with a graceful error- handling retry path in this same commit. If the inline data is cleared after locking the xattr, we safely release all resources (releasing iloc.bh, unlocking/putting the folio, stopping the active journal transaction handle) and return 0 (VFS retry) to let the generic write path retry the operation safely. Reported-by: syzbot+0c89d865531d053abb2d@syzkaller.appspotmail.com Closes: https://syzkaller.appspot.com/bug?extid=0c89d865531d053abb2d Fixes: 3fdcfb668fd7 ("ext4: add journalled write support for inline data") Suggested-by: Jan Kara Signed-off-by: Aditya Prakash Srivastava --- Changes in v3: - Changed EXT4_WRITE_DATA_INLINE to 4 (Bit 2) and treat fsdata as bitwise flags, allowing decoupling of independent states in the write path (e.g. standard fallback and inline writes), as suggested by Jan Kara. - Clear the EXT4_WRITE_DATA_INLINE bit on entry to ext4_write_begin() to safely unroll state for any VFS write retries. - Perform bitwise AND checks for EXT4_WRITE_DATA_INLINE and FALL_BACK_TO_NONDELALLOC flags in the write_end and da_write_end handlers. Changes in v2: - Folded the BUG_ON fix from the second patch into the first one to ensure bisectability across git history, as suggested by Jan Kara. - Removed the pointless initialization `*fsdata = NULL` on entry to `ext4_write_begin()`. - Removed the redundant check `if (fsdata)` in `ext4_write_begin()`. fs/ext4/ext4.h | 1 + fs/ext4/inline.c | 14 +++++++++++++- fs/ext4/inode.c | 24 +++++++++++++----------- 3 files changed, 27 insertions(+), 12 deletions(-) diff --git a/fs/ext4/ext4.h b/fs/ext4/ext4.h index b37c136ea3ab..9e6f6467bdeb 100644 --- a/fs/ext4/ext4.h +++ b/fs/ext4/ext4.h @@ -3138,6 +3138,7 @@ int do_journal_get_write_access(handle_t *handle, struct inode *inode, void ext4_set_inode_mapping_order(struct inode *inode); #define FALL_BACK_TO_NONDELALLOC 1 #define CONVERT_INLINE_DATA 2 +#define EXT4_WRITE_DATA_INLINE 4 typedef enum { EXT4_IGET_NORMAL = 0, diff --git a/fs/ext4/inline.c b/fs/ext4/inline.c index 8045e4ff270c..cfd591dc1d9c 100644 --- a/fs/ext4/inline.c +++ b/fs/ext4/inline.c @@ -812,7 +812,19 @@ int ext4_write_inline_data_end(struct inode *inode, loff_t pos, unsigned len, goto out; } ext4_write_lock_xattr(inode, &no_expand); - BUG_ON(!ext4_has_inline_data(inode)); + /* + * We could have raced with ext4_page_mkwrite() converting + * the inode and clearing the inline data flag, so we just + * release resources and retry the whole write. + */ + if (unlikely(!ext4_has_inline_data(inode))) { + ext4_write_unlock_xattr(inode, &no_expand); + brelse(iloc.bh); + folio_unlock(folio); + folio_put(folio); + ext4_journal_stop(handle); + return 0; + } /* * ei->i_inline_off may have changed since diff --git a/fs/ext4/inode.c b/fs/ext4/inode.c index ce99807c5f5b..4e1bf54e511d 100644 --- a/fs/ext4/inode.c +++ b/fs/ext4/inode.c @@ -1302,6 +1302,8 @@ static int ext4_write_begin(const struct kiocb *iocb, if (unlikely(ret)) return ret; + *fsdata = (void *)((unsigned long)*fsdata & ~EXT4_WRITE_DATA_INLINE); + trace_ext4_write_begin(inode, pos, len); /* * Reserve one block more for addition to orphan list in case @@ -1316,8 +1318,10 @@ static int ext4_write_begin(const struct kiocb *iocb, foliop); if (ret < 0) return ret; - if (ret == 1) + if (ret == 1) { + *fsdata = (void *)((unsigned long)*fsdata | EXT4_WRITE_DATA_INLINE); return 0; + } } /* @@ -1450,8 +1454,7 @@ static int ext4_write_end(const struct kiocb *iocb, trace_ext4_write_end(inode, pos, len, copied); - if (ext4_has_inline_data(inode) && - ext4_test_inode_state(inode, EXT4_STATE_MAY_INLINE_DATA)) + if ((unsigned long)fsdata & EXT4_WRITE_DATA_INLINE) return ext4_write_inline_data_end(inode, pos, len, copied, folio); @@ -1560,8 +1563,7 @@ static int ext4_journalled_write_end(const struct kiocb *iocb, BUG_ON(!ext4_handle_valid(handle)); - if (ext4_has_inline_data(inode) && - ext4_test_inode_state(inode, EXT4_STATE_MAY_INLINE_DATA)) + if ((unsigned long)fsdata & EXT4_WRITE_DATA_INLINE) return ext4_write_inline_data_end(inode, pos, len, copied, folio); @@ -3161,8 +3163,10 @@ static int ext4_da_write_begin(const struct kiocb *iocb, foliop, fsdata, true); if (ret < 0) return ret; - if (ret == 1) + if (ret == 1) { + *fsdata = (void *)((unsigned long)*fsdata | EXT4_WRITE_DATA_INLINE); return 0; + } } retry: @@ -3291,17 +3295,15 @@ static int ext4_da_write_end(const struct kiocb *iocb, struct folio *folio, void *fsdata) { struct inode *inode = mapping->host; - int write_mode = (int)(unsigned long)fsdata; + unsigned long write_mode = (unsigned long)fsdata; - if (write_mode == FALL_BACK_TO_NONDELALLOC) + if (write_mode & FALL_BACK_TO_NONDELALLOC) return ext4_write_end(iocb, mapping, pos, len, copied, folio, fsdata); trace_ext4_da_write_end(inode, pos, len, copied); - if (write_mode != CONVERT_INLINE_DATA && - ext4_test_inode_state(inode, EXT4_STATE_MAY_INLINE_DATA) && - ext4_has_inline_data(inode)) + if (write_mode & EXT4_WRITE_DATA_INLINE) return ext4_write_inline_data_end(inode, pos, len, copied, folio); -- 2.47.3