[PATCH 6.1 186/195] erofs: fix inconsistent per-file compression format

Greg Kroah-Hartman
2024-02-27T14:20:55Z

From: Gao Xiang <hsiangkao@linux.alibaba.com>

commit 118a8cf504d7dfa519562d000f423ee3ca75d2c4 upstream.

EROFS can select compression algorithms on a per-file basis, and each
per-file compression algorithm needs to be marked in the on-disk
superblock for initialization.

However, syzkaller can generate inconsistent crafted images that use
an unsupported algorithmtype for specific inodes, e.g. use MicroLZMA
algorithmtype even it's not set in `sbi->available_compr_algs`. This
can lead to an unexpected "BUG: kernel NULL pointer dereference" if
the corresponding decompressor isn't built-in.

Fix this by checking against `sbi->available_compr_algs` for each
m_algorithmformat request. Incorrect !erofs_sb_has_compr_cfgs preset
bitmap is now fixed together since it was harmless previously.

Reported-by: <bugreport@ubisectech.com>
Fixes: 8f89926290c4 ("erofs: get compression algorithms directly on mapping")
Fixes: 622ceaddb764 ("erofs: lzma compression support")
Reviewed-by: Yue Hu <huyue2@coolpad.com>
Link: https://lore.kernel.org/r/20240113150602.1471050-1-hsiangkao@linux.alibaba.com
Signed-off-by: Gao Xiang <hsiangkao@linux.alibaba.com>
Signed-off-by: Gao Xiang <hsiangkao@linux.alibaba.com>
Signed-off-by: Yue Hu <huyue2@coolpad.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
fs/erofs/decompressor.c | 2 +-
fs/erofs/zmap.c | 23 +++++++++++++----------
2 files changed, 14 insertions(+), 11 deletions(-)

--- a/fs/erofs/decompressor.c
+++ b/fs/erofs/decompressor.c
@@ -396,7 +396,7 @@ int z_erofs_parse_cfgs(struct super_bloc
int size, ret = 0;

if (!erofs_sb_has_compr_cfgs(sbi)) {
- sbi->available_compr_algs = Z_EROFS_COMPRESSION_LZ4;
+ sbi->available_compr_algs = 1 << Z_EROFS_COMPRESSION_LZ4;
return z_erofs_load_lz4_config(sb, dsb, NULL, 0);
}

--- a/fs/erofs/zmap.c
+++ b/fs/erofs/zmap.c
@@ -610,7 +610,7 @@ static int z_erofs_do_map_blocks(struct
.map = map,
};
int err = 0;
- unsigned int lclusterbits, endoff;
+ unsigned int lclusterbits, endoff, afmt;
unsigned long initial_lcn;
unsigned long long ofs, end;

@@ -700,17 +700,20 @@ static int z_erofs_do_map_blocks(struct
err = -EFSCORRUPTED;
goto unmap_out;
}
- if (vi->z_advise & Z_EROFS_ADVISE_INTERLACED_PCLUSTER)
- map->m_algorithmformat =
- Z_EROFS_COMPRESSION_INTERLACED;
- else
- map->m_algorithmformat =
- Z_EROFS_COMPRESSION_SHIFTED;
- } else if (m.headtype == Z_EROFS_VLE_CLUSTER_TYPE_HEAD2) {
- map->m_algorithmformat = vi->z_algorithmtype[1];
+ afmt = vi->z_advise & Z_EROFS_ADVISE_INTERLACED_PCLUSTER ?
+ Z_EROFS_COMPRESSION_INTERLACED :
+ Z_EROFS_COMPRESSION_SHIFTED;
} else {
- map->m_algorithmformat = vi->z_algorithmtype[0];
+ afmt = m.headtype == Z_EROFS_VLE_CLUSTER_TYPE_HEAD2 ?
+ vi->z_algorithmtype[1] : vi->z_algorithmtype[0];
+ if (!(EROFS_I_SB(inode)->available_compr_algs & (1 << afmt))) {
+ erofs_err(inode->i_sb, "inconsistent algorithmtype %u for nid %llu",
+ afmt, vi->nid);
+ err = -EFSCORRUPTED;
+ goto unmap_out;
+ }
}
+ map->m_algorithmformat = afmt;

if ((flags & EROFS_GET_BLOCKS_FIEMAP) ||
((flags & EROFS_GET_BLOCKS_READMORE) &&