CVE-2021-47275

published 2024-05-21

CVE-2021-47275: In the Linux kernel, the following vulnerability has been resolved: bcache: avoid oversized read request in cache missing code path In the cache missing code…

Priority P4 23 medium 5.5 CVSS 3.1

AV L AC L PR L UI N S U C N I N A H

In the Linux kernel, the following vulnerability has been resolved:

bcache: avoid oversized read request in cache missing code path

In the cache missing code path of cached device, if a proper location
from the internal B+ tree is matched for a cache miss range, function
cached_dev_cache_miss() will be called in cache_lookup_fn() in the
following code block,
[code block 1]
526 unsigned int sectors = KEY_INODE(k) == s->iop.inode
527 ? min_t(uint64_t, INT_MAX,
528 KEY_START(k) - bio->bi_iter.bi_sector)
529 : INT_MAX;
530 int ret = s->d->cache_miss(b, s, bio, sectors);

Here s->d->cache_miss() is the call backfunction pointer initialized as
cached_dev_cache_miss(), the last parameter 'sectors' is an important
hint to calculate the size of read request to backing device of the
missing cache data.

Current calculation in above code block may generate oversized value of
'sectors', which consequently may trigger 2 different potential kernel
panics by BUG() or BUG_ON() as listed below,

1) BUG_ON() inside bch_btree_insert_key(),
[code block 2]
886 BUG_ON(b->ops->is_extents && !KEY_SIZE(k));
2) BUG() inside biovec_slab(),
[code block 3]
51 default:
52 BUG();
53 return NULL;

All the above panics are original from cached_dev_cache_miss() by the
oversized parameter 'sectors'.

Inside cached_dev_cache_miss(), parameter 'sectors' is used to calculate
the size of data read from backing device for the cache missing. This
size is stored in s->insert_bio_sectors by the following lines of code,
[code block 4]
909 s->insert_bio_sectors = min(sectors, bio_sectors(bio) + reada);

Then the actual key inserting to the internal B+ tree is generated and
stored in s->iop.replace_key by the following lines of code,
[code block 5]
911 s->iop.replace_key = KEY(s->iop.inode,
912 bio->bi_iter.bi_sector + s->insert_bio_sectors,
913 s->insert_bio_sectors);
The oversized parameter 'sectors' may trigger panic 1) by BUG_ON() from
the above code block.

And the bio sending to backing device for the m

Affected

9 ranges

Vendor	Product	Version range	Fixed in
debian	linux	< linux 5.14.6-1 (bookworm)	linux 5.14.6-1 (bookworm)
linux	linux	—	—
linux	linux	>= cafe563591446cf80bfbc2fe3bc72a2e36cf1060 < 555002a840ab88468e252b0eedf0b05e2ce7099c	555002a840ab88468e252b0eedf0b05e2ce7099c
linux	linux	>= cafe563591446cf80bfbc2fe3bc72a2e36cf1060 < 41fe8d088e96472f63164e213de44ec77be69478	41fe8d088e96472f63164e213de44ec77be69478
linux	linux_kernel	< 5.12.11	5.12.11
linux	linux_kernel	—	—
linux	linux_kernel	>= 0 < 5.14.6-1	5.14.6-1
linux	linux_kernel	>= 0 < 5.14.6-1	5.14.6-1
linux	linux_kernel	>= 0 < 5.14.6-1	5.14.6-1

CVSS provenance

nvd v3.1 5.5 MEDIUM CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H

osv 5.5 MEDIUM

vendor_debian 5.5 MEDIUM

vendor_redhat 5.5 MEDIUM

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