xf86pciBus: replace on thread-safe strtok_r in xf86ParsePciBusString() #1415
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- Thread A calls xf86ParsePciBusString("PCI:1@0:2:3 "). Execution of strtok_r (in the patched version) or strtok (in the vulnerable version) is suspended after the first call, when the internal pointer is set to the rest of the string ":2:3".
- Thread B (the attacker's thread) calls another function in the X server that also uses strtok (for example, to parse another configuration string). This call overwrites the internal static state of strtok.
- Thread A resumes and calls strtok(NULL, ":") again. Instead of getting the token "2" from the source string, it will receive data from the string processed by Thread B, or NULL, which will lead to incorrect BusID parsing, potential failure, or other unpredictable behavior.
Applying patch with strtok_r completely eliminates this category of vulnerabilities in multithreaded scenarios.
algrid
reviewed
Nov 17, 2025
| s = Xstrdup(id); | ||
| p = strtok(s, ":"); | ||
| s = last = Xstrdup(id); | ||
| p = strtok_r(last, ":", &last); |
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Is there a particular reason to use last for both the first and the last argument?
I thought the typical usage would be something like
char *last;
p = strtok_r(s, ":", &last);
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Related to issue: #1398
Applying patch with strtok_r completely eliminates this category of vulnerabilities in multithreaded scenarios.