Re: FAILED: patch "[PATCH] dm-integrity: don't modify bio's immutable bio_vec in" failed to apply to 5.15-stable tree

[Mikulas Patocka <mpatocka@xxxxxxxxxx>]

On Sat, 30 Dec 2023, gregkh@xxxxxxxxxxxxxxxxxxx wrote:

> 
> The patch below does not apply to the 5.15-stable tree.
> If someone wants it applied there, or to any other stable or longterm
> tree, then please email the backport, including the original git commit
> id to <stable@xxxxxxxxxxxxxxx>.

Hi

Here I'm sending backport of the patch 
b86f4b790c998afdbc88fe1aa55cfe89c4068726 for the stable branches 4.19 to 
5.15.

commit b86f4b790c998afdbc88fe1aa55cfe89c4068726
Author: Mikulas Patocka <mpatocka@xxxxxxxxxx>
Date:   Tue Dec 5 16:39:16 2023 +0100

    dm-integrity: don't modify bio's immutable bio_vec in integrity_metadata()
    
    __bio_for_each_segment assumes that the first struct bio_vec argument
    doesn't change - it calls "bio_advance_iter_single((bio), &(iter),
    (bvl).bv_len)" to advance the iterator. Unfortunately, the dm-integrity
    code changes the bio_vec with "bv.bv_len -= pos". When this code path
    is taken, the iterator would be out of sync and dm-integrity would
    report errors. This happens if the machine is out of memory and
    "kmalloc" fails.
    
    Fix this bug by making a copy of "bv" and changing the copy instead.
    
    Fixes: 7eada909bfd7 ("dm: add integrity target")
    Cc: stable@xxxxxxxxxxxxxxx      # v4.12+
    Signed-off-by: Mikulas Patocka <mpatocka@xxxxxxxxxx>
    Signed-off-by: Mike Snitzer <snitzer@xxxxxxxxxx>

---
 drivers/md/dm-integrity.c |   11 ++++++-----
 1 file changed, 6 insertions(+), 5 deletions(-)

Index: linux-stable/drivers/md/dm-integrity.c
===================================================================
--- linux-stable.orig/drivers/md/dm-integrity.c
+++ linux-stable/drivers/md/dm-integrity.c
@@ -1762,11 +1762,12 @@ static void integrity_metadata(struct wo
 		sectors_to_process = dio->range.n_sectors;
 
 		__bio_for_each_segment(bv, bio, iter, dio->bio_details.bi_iter) {
+			struct bio_vec bv_copy = bv;
 			unsigned pos;
 			char *mem, *checksums_ptr;
 
 again:
-			mem = (char *)kmap_atomic(bv.bv_page) + bv.bv_offset;
+			mem = (char *)kmap_atomic(bv_copy.bv_page) + bv_copy.bv_offset;
 			pos = 0;
 			checksums_ptr = checksums;
 			do {
@@ -1775,7 +1776,7 @@ again:
 				sectors_to_process -= ic->sectors_per_block;
 				pos += ic->sectors_per_block << SECTOR_SHIFT;
 				sector += ic->sectors_per_block;
-			} while (pos < bv.bv_len && sectors_to_process && checksums != checksums_onstack);
+			} while (pos < bv_copy.bv_len && sectors_to_process && checksums != checksums_onstack);
 			kunmap_atomic(mem);
 
 			r = dm_integrity_rw_tag(ic, checksums, &dio->metadata_block, &dio->metadata_offset,
@@ -1796,9 +1797,9 @@ again:
 			if (!sectors_to_process)
 				break;
 
-			if (unlikely(pos < bv.bv_len)) {
-				bv.bv_offset += pos;
-				bv.bv_len -= pos;
+			if (unlikely(pos < bv_copy.bv_len)) {
+				bv_copy.bv_offset += pos;
+				bv_copy.bv_len -= pos;
 				goto again;
 			}
 		}