[PATCH AUTOSEL 6.0 09/16] nilfs2: fix shift-out-of-bounds/overflow in nilfs_sb2_bad_offset()

[PATCH AUTOSEL 6.0 09/16] nilfs2: fix shift-out-of-bounds/overflow in nilfs_sb2_bad_offset()

[Sasha Levin]

From: Ryusuke Konishi <konishi.ryusuke-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org>

[ Upstream commit 610a2a3d7d8be3537458a378ec69396a76c385b6 ]

Patch series "nilfs2: fix UBSAN shift-out-of-bounds warnings on mount
time".

The first patch fixes a bug reported by syzbot, and the second one fixes
the remaining bug of the same kind.  Although they are triggered by the
same super block data anomaly, I divided it into the above two because the
details of the issues and how to fix it are different.

Both are required to eliminate the shift-out-of-bounds issues at mount
time.

This patch (of 2):

If the block size exponent information written in an on-disk superblock is
corrupted, nilfs_sb2_bad_offset helper function can trigger
shift-out-of-bounds warning followed by a kernel panic (if panic_on_warn
is set):

 shift exponent 38983 is too large for 64-bit type 'unsigned long long'
 Call Trace:
  <TASK>
  __dump_stack lib/dump_stack.c:88 [inline]
  dump_stack_lvl+0x1b1/0x28e lib/dump_stack.c:106
  ubsan_epilogue lib/ubsan.c:151 [inline]
  __ubsan_handle_shift_out_of_bounds+0x33d/0x3b0 lib/ubsan.c:322
  nilfs_sb2_bad_offset fs/nilfs2/the_nilfs.c:449 [inline]
  nilfs_load_super_block+0xdf5/0xe00 fs/nilfs2/the_nilfs.c:523
  init_nilfs+0xb7/0x7d0 fs/nilfs2/the_nilfs.c:577
  nilfs_fill_super+0xb1/0x5d0 fs/nilfs2/super.c:1047
  nilfs_mount+0x613/0x9b0 fs/nilfs2/super.c:1317
  ...

In addition, since nilfs_sb2_bad_offset() performs multiplication without
considering the upper bound, the computation may overflow if the disk
layout parameters are not normal.

This fixes these issues by inserting preliminary sanity checks for those
parameters and by converting the comparison from one involving
multiplication and left bit-shifting to one using division and right
bit-shifting.

Link: https://lkml.kernel.org/r/20221027044306.42774-1-konishi.ryusuke-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org
Link: https://lkml.kernel.org/r/20221027044306.42774-2-konishi.ryusuke-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org
Signed-off-by: Ryusuke Konishi <konishi.ryusuke-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org>
Reported-by: syzbot+e91619dd4c11c4960706-Pl5Pbv+GP7P466ipTTIvnc23WoclnBCfAL8bYrjMMd8@public.gmane.org
Tested-by: Ryusuke Konishi <konishi.ryusuke-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org>
Signed-off-by: Andrew Morton <akpm-de/tnXTf+JLsfHDXvbKv3WD2FQJk+8+b@public.gmane.org>
Signed-off-by: Sasha Levin <sashal-DgEjT+Ai2ygdnm+yROfE0A@public.gmane.org>
---
 fs/nilfs2/the_nilfs.c | 31 +++++++++++++++++++++++++++----
 1 file changed, 27 insertions(+), 4 deletions(-)

diff --git a/fs/nilfs2/the_nilfs.c b/fs/nilfs2/the_nilfs.c
index c8b89b4f94e0..a7c829a7d4f1 100644
--- a/fs/nilfs2/the_nilfs.c
+++ b/fs/nilfs2/the_nilfs.c
@@ -13,6 +13,7 @@
 #include <linux/blkdev.h>
 #include <linux/backing-dev.h>
 #include <linux/random.h>
+#include <linux/log2.h>
 #include <linux/crc32.h>
 #include "nilfs.h"
 #include "segment.h"
@@ -443,11 +444,33 @@ static int nilfs_valid_sb(struct nilfs_super_block *sbp)
 	return crc == le32_to_cpu(sbp->s_sum);
 }
 
-static int nilfs_sb2_bad_offset(struct nilfs_super_block *sbp, u64 offset)
+/**
+ * nilfs_sb2_bad_offset - check the location of the second superblock
+ * @sbp: superblock raw data buffer
+ * @offset: byte offset of second superblock calculated from device size
+ *
+ * nilfs_sb2_bad_offset() checks if the position on the second
+ * superblock is valid or not based on the filesystem parameters
+ * stored in @sbp.  If @offset points to a location within the segment
+ * area, or if the parameters themselves are not normal, it is
+ * determined to be invalid.
+ *
+ * Return Value: true if invalid, false if valid.
+ */
+static bool nilfs_sb2_bad_offset(struct nilfs_super_block *sbp, u64 offset)
 {
-	return offset < ((le64_to_cpu(sbp->s_nsegments) *
-			  le32_to_cpu(sbp->s_blocks_per_segment)) <<
-			 (le32_to_cpu(sbp->s_log_block_size) + 10));
+	unsigned int shift_bits = le32_to_cpu(sbp->s_log_block_size);
+	u32 blocks_per_segment = le32_to_cpu(sbp->s_blocks_per_segment);
+	u64 nsegments = le64_to_cpu(sbp->s_nsegments);
+	u64 index;
+
+	if (blocks_per_segment < NILFS_SEG_MIN_BLOCKS ||
+	    shift_bits > ilog2(NILFS_MAX_BLOCK_SIZE) - BLOCK_SIZE_BITS)
+		return true;
+
+	index = offset >> (shift_bits + BLOCK_SIZE_BITS);
+	do_div(index, blocks_per_segment);
+	return index < nsegments;
 }
 
 static void nilfs_release_super_block(struct the_nilfs *nilfs)
-- 
2.35.1

[PATCH AUTOSEL 6.0 10/16] nilfs2: fix shift-out-of-bounds due to too large exponent of block size

[Sasha Levin]

From: Ryusuke Konishi <konishi.ryusuke@gmail.com>

[ Upstream commit ebeccaaef67a4895d2496ab8d9c2fb8d89201211 ]

If field s_log_block_size of superblock data is corrupted and too large,
init_nilfs() and load_nilfs() still can trigger a shift-out-of-bounds
warning followed by a kernel panic (if panic_on_warn is set):

 shift exponent 38973 is too large for 32-bit type 'int'
 Call Trace:
  <TASK>
  dump_stack_lvl+0xcd/0x134
  ubsan_epilogue+0xb/0x50
  __ubsan_handle_shift_out_of_bounds.cold.12+0x17b/0x1f5
  init_nilfs.cold.11+0x18/0x1d [nilfs2]
  nilfs_mount+0x9b5/0x12b0 [nilfs2]
  ...

This fixes the issue by adding and using a new helper function for getting
block size with sanity check.

Link: https://lkml.kernel.org/r/20221027044306.42774-3-konishi.ryusuke@gmail.com
Signed-off-by: Ryusuke Konishi <konishi.ryusuke@gmail.com>
Tested-by: Ryusuke Konishi <konishi.ryusuke@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
 fs/nilfs2/the_nilfs.c | 42 ++++++++++++++++++++++++++++++++++++++----
 1 file changed, 38 insertions(+), 4 deletions(-)

diff --git a/fs/nilfs2/the_nilfs.c b/fs/nilfs2/the_nilfs.c
index a7c829a7d4f1..2064e6473d30 100644
--- a/fs/nilfs2/the_nilfs.c
+++ b/fs/nilfs2/the_nilfs.c
@@ -193,6 +193,34 @@ static int nilfs_store_log_cursor(struct the_nilfs *nilfs,
 	return ret;
 }
 
+/**
+ * nilfs_get_blocksize - get block size from raw superblock data
+ * @sb: super block instance
+ * @sbp: superblock raw data buffer
+ * @blocksize: place to store block size
+ *
+ * nilfs_get_blocksize() calculates the block size from the block size
+ * exponent information written in @sbp and stores it in @blocksize,
+ * or aborts with an error message if it's too large.
+ *
+ * Return Value: On success, 0 is returned. If the block size is too
+ * large, -EINVAL is returned.
+ */
+static int nilfs_get_blocksize(struct super_block *sb,
+			       struct nilfs_super_block *sbp, int *blocksize)
+{
+	unsigned int shift_bits = le32_to_cpu(sbp->s_log_block_size);
+
+	if (unlikely(shift_bits >
+		     ilog2(NILFS_MAX_BLOCK_SIZE) - BLOCK_SIZE_BITS)) {
+		nilfs_err(sb, "too large filesystem blocksize: 2 ^ %u KiB",
+			  shift_bits);
+		return -EINVAL;
+	}
+	*blocksize = BLOCK_SIZE << shift_bits;
+	return 0;
+}
+
 /**
  * load_nilfs - load and recover the nilfs
  * @nilfs: the_nilfs structure to be released
@@ -246,11 +274,15 @@ int load_nilfs(struct the_nilfs *nilfs, struct super_block *sb)
 		nilfs->ns_sbwtime = le64_to_cpu(sbp[0]->s_wtime);
 
 		/* verify consistency between two super blocks */
-		blocksize = BLOCK_SIZE << le32_to_cpu(sbp[0]->s_log_block_size);
+		err = nilfs_get_blocksize(sb, sbp[0], &blocksize);
+		if (err)
+			goto scan_error;
+
 		if (blocksize != nilfs->ns_blocksize) {
 			nilfs_warn(sb,
 				   "blocksize differs between two super blocks (%d != %d)",
 				   blocksize, nilfs->ns_blocksize);
+			err = -EINVAL;
 			goto scan_error;
 		}
 
@@ -609,9 +641,11 @@ int init_nilfs(struct the_nilfs *nilfs, struct super_block *sb, char *data)
 	if (err)
 		goto failed_sbh;
 
-	blocksize = BLOCK_SIZE << le32_to_cpu(sbp->s_log_block_size);
-	if (blocksize < NILFS_MIN_BLOCK_SIZE ||
-	    blocksize > NILFS_MAX_BLOCK_SIZE) {
+	err = nilfs_get_blocksize(sb, sbp, &blocksize);
+	if (err)
+		goto failed_sbh;
+
+	if (blocksize < NILFS_MIN_BLOCK_SIZE) {
 		nilfs_err(sb,
 			  "couldn't mount because of unsupported filesystem blocksize %d",
 			  blocksize);
-- 
2.35.1