CVE-2022-49648 Information

Mar 01, 2025 cve

Description

In the Linux kernel the following vulnerability has been resolved:

tracing/histograms: Fix memory leak problem

This reverts commit 46bbe5c671e06f070428b9be142cc4ee5cedebac.

As commit 46bbe5c671e0 ( racing: fix double free) said the \double free\ problem reported by clang static analyzer is:

In parse_var_defs() if there is a problem allocating var_defs.expr the earlier var_defs.name is freed. This free is duplicated by free_var_defs() which frees the rest of the list.

However if there is a problem allocating N-th var_defs.expr:

  • in parse_var_defs() the freed ’earlier var_defs.name’ is actually the N-th var_defs.name;

  • then in free_var_defs() the names from 0th to (N-1)-th are freed;

                    IF ALLOCATING PROBLEM HAPPENED HERE!!! -+
                                                         \
                                                          |
  0th           1th                 (N-1)-th      N-th    V
  +-------------+-------------+-----+-------------+-----------

var_defs: | name | expr | name | expr | … | name | expr | name | /// +————-+————-+—–+————-+———–

These two frees don’t act on same name so there was no \double free\nproblem before. Conversely after that commit we get a \memory leak\nproblem because the above \N-th var_defs.name\ is not freed.

If enable CONFIG_DEBUG_KMEMLEAK and inject a fault at where the N-th var_defs.expr allocated then execute on shell like: $ echo ‘hist:key=call_site:val=$v1$v2:v1=bytes_reqv2=bytes_alloc’ >
/sys/kernel/debug/tracing/events/kmem/kmalloc/trigger

Then kmemleak reports: unreferenced object 0xffff8fb100ef3518 (size 8): comm ash\ pid 196 jiffies 4295681690 (age 28.538s) hex dump (first 8 bytes): 76 31 00 00 b1 8f ff ff v1…… backtrace: [<0000000038fe4895>] kstrdup+0x2d/0x60 [<00000000c99c049a>] event_hist_trigger_parse+0x206f/0x20e0 [<00000000ae70d2cc>] trigger_process_regex+0xc0/0x110 [<0000000066737a4c>] event_trigger_write+0x75/0xd0 [<000000007341e40c>] vfs_write+0xbb/0x2a0 [<0000000087fde4c2>] ksys_write+0x59/0xd0 [<00000000581e9cdf>] do_syscall_64+0x3a/0x80 [<00000000cf3b065c>] entry_SYSCALL_64_after_hwframe+0x46/0xb0

Reference

https://git.kernel.org/stable/c/22eeff55679d9e7c0f768c79bfbd83e2f8142d89 https://git.kernel.org/stable/c/4d453eb5e1eec89971aa5b3262857ee26cfdffd3 https://git.kernel.org/stable/c/78a1400c42ee11197eb1f0f85ba51df9a4fdfff0 https://git.kernel.org/stable/c/7edc3945bdce9c39198a10d6129377a5c53559c2 https://git.kernel.org/stable/c/eb622d5580b9e2ff694f62da6410618bd73853cb https://git.kernel.org/stable/c/ecc6dec12c33aa92c086cd702af9f544ddaf3c75

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