Bug 2373523 (CVE-2022-49978)

Summary: CVE-2022-49978 kernel: fbdev: fb_pm2fb: Avoid potential divide by zero error
Product: [Other] Security Response Reporter: OSIDB Bzimport <bzimport>
Component: vulnerabilityAssignee: Product Security DevOps Team <prodsec-dev>
Status: NEW --- QA Contact:
Severity: medium Docs Contact:
Priority: medium    
Version: unspecifiedCC: dfreiber, drow, jburrell, vkumar
Target Milestone: ---Keywords: Security
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Hardware: All   
OS: Linux   
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oVirt Team: --- RHEL 7.3 requirements from Atomic Host:
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Description OSIDB Bzimport 2025-06-18 12:06:44 UTC 
In the Linux kernel, the following vulnerability has been resolved:

fbdev: fb_pm2fb: Avoid potential divide by zero error

In `do_fb_ioctl()` of fbmem.c, if cmd is FBIOPUT_VSCREENINFO, var will be
copied from user, then go through `fb_set_var()` and
`info->fbops->fb_check_var()` which could may be `pm2fb_check_var()`.
Along the path, `var->pixclock` won't be modified. This function checks
whether reciprocal of `var->pixclock` is too high. If `var->pixclock` is
zero, there will be a divide by zero error. So, it is necessary to check
whether denominator is zero to avoid crash. As this bug is found by
Syzkaller, logs are listed below.

divide error in pm2fb_check_var
Call Trace:
 <TASK>
 fb_set_var+0x367/0xeb0 drivers/video/fbdev/core/fbmem.c:1015
 do_fb_ioctl+0x234/0x670 drivers/video/fbdev/core/fbmem.c:1110
 fb_ioctl+0xdd/0x130 drivers/video/fbdev/core/fbmem.c:1189
Comment 1 Avinash Hanwate 2025-06-19 18:13:49 UTC 
Upstream advisory:
https://lore.kernel.org/linux-cve-announce/2025061820-CVE-2022-49978-8dc2@gregkh/T