From: Eric Biggers ebiggers@google.com

As is done elsewhere in the file, build the struct ext4_fc_tl on the stack and memcpy() it into the buffer, rather than directly writing it to a potentially-unaligned location in the buffer.

Fixes: aa75f4d3daae ("ext4: main fast-commit commit path") Cc: stable@vger.kernel.org # v5.10+ Signed-off-by: Eric Biggers ebiggers@google.com --- fs/ext4/fast_commit.c | 39 +++++++++++++++++++++------------------ 1 file changed, 21 insertions(+), 18 deletions(-)

diff --git a/fs/ext4/fast_commit.c b/fs/ext4/fast_commit.c index d5ad4b2b235d6..892fa7c7a768b 100644 --- a/fs/ext4/fast_commit.c +++ b/fs/ext4/fast_commit.c @@ -675,6 +675,15 @@ static void ext4_fc_submit_bh(struct super_block *sb, bool is_tail)

/* Ext4 commit path routines */

+/* memcpy to fc reserved space and update CRC */ +static void *ext4_fc_memcpy(struct super_block *sb, void *dst, const void *src, + int len, u32 *crc) +{ + if (crc) + *crc = ext4_chksum(EXT4_SB(sb), *crc, src, len); + return memcpy(dst, src, len); +} + /* memzero and update CRC */ static void *ext4_fc_memzero(struct super_block *sb, void *dst, int len, u32 *crc) @@ -700,12 +709,13 @@ static void *ext4_fc_memzero(struct super_block *sb, void *dst, int len, */ static u8 *ext4_fc_reserve_space(struct super_block *sb, int len, u32 *crc) { - struct ext4_fc_tl *tl; + struct ext4_fc_tl tl; struct ext4_sb_info *sbi = EXT4_SB(sb); struct buffer_head *bh; int bsize = sbi->s_journal->j_blocksize; int ret, off = sbi->s_fc_bytes % bsize; int pad_len; + u8 *dst;

/* * After allocating len, we should have space at least for a 0 byte @@ -729,16 +739,18 @@ static u8 *ext4_fc_reserve_space(struct super_block *sb, int len, u32 *crc) return sbi->s_fc_bh->b_data + off; } /* Need to add PAD tag */ - tl = (struct ext4_fc_tl *)(sbi->s_fc_bh->b_data + off); - tl->fc_tag = cpu_to_le16(EXT4_FC_TAG_PAD); + dst = sbi->s_fc_bh->b_data + off; + tl.fc_tag = cpu_to_le16(EXT4_FC_TAG_PAD); pad_len = bsize - off - 1 - EXT4_FC_TAG_BASE_LEN; - tl->fc_len = cpu_to_le16(pad_len); - if (crc) - *crc = ext4_chksum(sbi, *crc, tl, EXT4_FC_TAG_BASE_LEN); - if (pad_len > 0) - ext4_fc_memzero(sb, tl + 1, pad_len, crc); + tl.fc_len = cpu_to_le16(pad_len); + ext4_fc_memcpy(sb, dst, &tl, EXT4_FC_TAG_BASE_LEN, crc); + dst += EXT4_FC_TAG_BASE_LEN; + if (pad_len > 0) { + ext4_fc_memzero(sb, dst, pad_len, crc); + dst += pad_len; + } /* Don't leak uninitialized memory in the unused last byte. */ - *((u8 *)(tl + 1) + pad_len) = 0; + *dst = 0;

ext4_fc_submit_bh(sb, false);

@@ -750,15 +762,6 @@ static u8 *ext4_fc_reserve_space(struct super_block *sb, int len, u32 *crc) return sbi->s_fc_bh->b_data; }

-/* memcpy to fc reserved space and update CRC */ -static void *ext4_fc_memcpy(struct super_block *sb, void *dst, const void *src, - int len, u32 *crc) -{ - if (crc) - *crc = ext4_chksum(EXT4_SB(sb), *crc, src, len); - return memcpy(dst, src, len); -} - /* * Complete a fast commit by writing tail tag. *