7.3-stable review patch. If anyone has any objections, please let me know. ------------------ From: Gyokhan Kochmarla [ Upstream commit 90b7e4a7a16443d9f6807b5c1dde52074d9f74c0 ] z_erofs_load_lz4_config() rejects a valid LZ4 image when the kernel's page size differs from the image's block size. It bounds the on-disk max_pclusterblks with erofs_blknr(sb, Z_EROFS_PCLUSTER_MAX_SIZE), which expands to Z_EROFS_PCLUSTER_MAX_SIZE >> sb->s_blocksize_bits. At the point this runs, sb->s_blocksize_bits still holds PAGE_SHIFT: erofs_fc_fill_super() seeds s_blocksize_bits to PAGE_SHIFT before reading the superblock, and only corrects it down to the on-disk blkszbits after erofs_read_superblock() returns. The LZ4 config is parsed inside erofs_read_superblock(), before that correction, so the bound is computed with the wrong shift. On a 64K-page kernel mounting a 4K-block image (e.g. one built with mkfs.erofs -C 262144 on a 4K-page host), the bound evaluates to 1 MiB >> 16 = 16 blocks instead of the correct 1 MiB >> 12 = 256 blocks. The image's legitimate max_pclusterblks of 64 then fails the check, mount returns -EINVAL, and booting from such an image as the root filesystem panics: erofs (device dm-0): too large lz4 pclusterblks 64 Kernel panic - not syncing: VFS: Unable to mount root fs sbi->blkszbits already holds the on-disk block size at this point, so compute the bound from it directly. This makes the check independent of the host page size and of superblock-parse ordering. commit 3acea5fc3354 ("erofs: avoid hardcoded blocksize for subpage block support") already handled the same ordering hazard for the superblock checksum path by using sbi->blkszbits in erofs_superblock_csum_verify(); the lz4 config path was missed. Fixes: 3acea5fc3354 ("erofs: avoid hardcoded blocksize for subpage block support") Cc: stable@vger.kernel.org Assisted-by: Kirocrew:gpt-5.6-sol Signed-off-by: Gyokhan Kochmarla Reviewed-by: Gao Xiang Signed-off-by: Gao Xiang Signed-off-by: Sasha Levin --- fs/erofs/decompressor.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/fs/erofs/decompressor.c b/fs/erofs/decompressor.c index d387b27c4ee21..771d862afc2ed 100644 --- a/fs/erofs/decompressor.c +++ b/fs/erofs/decompressor.c @@ -23,7 +23,7 @@ static int z_erofs_load_lz4_config(struct super_block *sb, if (!sbi->lz4.max_pclusterblks) { sbi->lz4.max_pclusterblks = 1; /* reserved case */ } else if (sbi->lz4.max_pclusterblks > - erofs_blknr(sb, Z_EROFS_PCLUSTER_MAX_SIZE)) { + Z_EROFS_PCLUSTER_MAX_SIZE >> sbi->blkszbits) { erofs_err(sb, "too large lz4 pclusterblks %u", sbi->lz4.max_pclusterblks); return -EINVAL; -- 2.53.0