erofs: fix invalid algorithm for encoded extents

The current algorithm sanity checks do not properly apply to new
encoded extents.

Unify the algorithm check with Z_EROFS_COMPRESSION(_RUNTIME)_MAX
and ensure consistency with sbi->available_compr_algs.

Reported-and-tested-by: syzbot+5a398eb460ddaa6f242f@syzkaller.appspotmail.com
Closes: https://lore.kernel.org/r/68a8bd20.050a0220.37038e.005a.GAE@google.com
Fixes: 1d191b4 ("erofs: implement encoded extent metadata")
Thanks-to: Edward Adam Davis <eadavis@qq.com>
Signed-off-by: Gao Xiang <hsiangkao@linux.alibaba.com>

Author: hsiangkao

fs/erofs/zmap.c

@@ -394,10 +394,10 @@ static int z_erofs_map_blocks_fo(struct inode *inode,
 		.map = map,
 		.in_mbox = erofs_inode_in_metabox(inode),
 	};
-	int err = 0;
-	unsigned int endoff, afmt;
+	unsigned int endoff;
 	unsigned long initial_lcn;
 	unsigned long long ofs, end;
+	int err;
 
 	ofs = flags & EROFS_GET_BLOCKS_FINDTAIL ? inode->i_size - 1 : map->m_la;
 	if (fragment && !(flags & EROFS_GET_BLOCKS_FINDTAIL) &&
@@ -482,20 +482,15 @@ static int z_erofs_map_blocks_fo(struct inode *inode,
 			err = -EFSCORRUPTED;
 			goto unmap_out;
 		}
-		afmt = vi->z_advise & Z_EROFS_ADVISE_INTERLACED_PCLUSTER ?
-			Z_EROFS_COMPRESSION_INTERLACED :
-			Z_EROFS_COMPRESSION_SHIFTED;
+		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_LCLUSTER_TYPE_HEAD2) {
+		map->m_algorithmformat = vi->z_algorithmtype[1];
 	} else {
-		afmt = m.headtype == Z_EROFS_LCLUSTER_TYPE_HEAD2 ?
-			vi->z_algorithmtype[1] : vi->z_algorithmtype[0];
-		if (!(EROFS_I_SB(inode)->available_compr_algs & (1 << afmt))) {
-			erofs_err(sb, "inconsistent algorithmtype %u for nid %llu",
-				  afmt, vi->nid);
-			err = -EFSCORRUPTED;
-			goto unmap_out;
-		}
+		map->m_algorithmformat = vi->z_algorithmtype[0];
 	}
-	map->m_algorithmformat = afmt;
 
 	if ((flags & EROFS_GET_BLOCKS_FIEMAP) ||
 	    ((flags & EROFS_GET_BLOCKS_READMORE) &&
@@ -626,9 +621,9 @@ static int z_erofs_fill_inode(struct inode *inode, struct erofs_map_blocks *map)
 {
 	struct erofs_inode *const vi = EROFS_I(inode);
 	struct super_block *const sb = inode->i_sb;
-	int err, headnr;
-	erofs_off_t pos;
 	struct z_erofs_map_header *h;
+	erofs_off_t pos;
+	int err = 0;
 
 	if (test_bit(EROFS_I_Z_INITED_BIT, &vi->flags)) {
 		/*
@@ -642,7 +637,6 @@ static int z_erofs_fill_inode(struct inode *inode, struct erofs_map_blocks *map)
 	if (wait_on_bit_lock(&vi->flags, EROFS_I_BL_Z_BIT, TASK_KILLABLE))
 		return -ERESTARTSYS;
 
-	err = 0;
 	if (test_bit(EROFS_I_Z_INITED_BIT, &vi->flags))
 		goto out_unlock;
 
@@ -679,15 +673,6 @@ static int z_erofs_fill_inode(struct inode *inode, struct erofs_map_blocks *map)
 	else if (vi->z_advise & Z_EROFS_ADVISE_INLINE_PCLUSTER)
 		vi->z_idata_size = le16_to_cpu(h->h_idata_size);
 
-	headnr = 0;
-	if (vi->z_algorithmtype[0] >= Z_EROFS_COMPRESSION_MAX ||
-	    vi->z_algorithmtype[++headnr] >= Z_EROFS_COMPRESSION_MAX) {
-		erofs_err(sb, "unknown HEAD%u format %u for nid %llu, please upgrade kernel",
-			  headnr + 1, vi->z_algorithmtype[headnr], vi->nid);
-		err = -EOPNOTSUPP;
-		goto out_unlock;
-	}
-
 	if (!erofs_sb_has_big_pcluster(EROFS_SB(sb)) &&
 	    vi->z_advise & (Z_EROFS_ADVISE_BIG_PCLUSTER_1 |
 			    Z_EROFS_ADVISE_BIG_PCLUSTER_2)) {
@@ -726,6 +711,30 @@ static int z_erofs_fill_inode(struct inode *inode, struct erofs_map_blocks *map)
 	return err;
 }
 
+static int z_erofs_map_sanity_check(struct inode *inode,
+				    struct erofs_map_blocks *map)
+{
+	struct erofs_sb_info *sbi = EROFS_I_SB(inode);
+
+	if (!(map->m_flags & EROFS_MAP_ENCODED))
+		return 0;
+	if (unlikely(map->m_algorithmformat >= Z_EROFS_COMPRESSION_RUNTIME_MAX)) {
+		erofs_err(inode->i_sb, "unknown algorithm %d @ pos %llu for nid %llu, please upgrade kernel",
+			  map->m_algorithmformat, map->m_la, EROFS_I(inode)->nid);
+		return -EOPNOTSUPP;
+	}
+	if (unlikely(map->m_algorithmformat < Z_EROFS_COMPRESSION_MAX &&
+		     !(sbi->available_compr_algs & (1 << map->m_algorithmformat)))) {
+		erofs_err(inode->i_sb, "inconsistent algorithmtype %u for nid %llu",
+			  map->m_algorithmformat, EROFS_I(inode)->nid);
+		return -EFSCORRUPTED;
+	}
+	if (unlikely(map->m_plen > Z_EROFS_PCLUSTER_MAX_SIZE ||
+		     map->m_llen > Z_EROFS_PCLUSTER_MAX_DSIZE))
+		return -EOPNOTSUPP;
+	return 0;
+}
+
 int z_erofs_map_blocks_iter(struct inode *inode, struct erofs_map_blocks *map,
 			    int flags)
 {
@@ -746,10 +755,8 @@ int z_erofs_map_blocks_iter(struct inode *inode, struct erofs_map_blocks *map,
 			else
 				err = z_erofs_map_blocks_fo(inode, map, flags);
 		}
-		if (!err && (map->m_flags & EROFS_MAP_ENCODED) &&
-		    unlikely(map->m_plen > Z_EROFS_PCLUSTER_MAX_SIZE ||
-			     map->m_llen > Z_EROFS_PCLUSTER_MAX_DSIZE))
-			err = -EOPNOTSUPP;
+		if (!err)
+			err = z_erofs_map_sanity_check(inode, map);
 		if (err)
 			map->m_llen = 0;
 	}