proc/linux: Don't open mmapped files before checking stat results #2002
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Instead of checking the filesystem containing the mapped file against specific magic device numbers, we use stat(2) before actually opening the file. (The open call can block on certain device nodes as reported in VirusTotal#1929.) To overcome the possible TOCTOU issue between stat() and open(), we double-check device, inode after we have opened the file. This also reverts commit 50eeef4. The original problem could also have been fixed by passing O_PATH to open(2). However, there seems to be no way to atomically upgrade those path-only fds to real file descriptors that we can mmap or read from, so this would not helped in overcoming the TOCTOU issue.
plusvic
approved these changes
Nov 7, 2023
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Instead of checking the filesystem containing the mapped file against specific magic device numbers, we use stat(2) before actually opening the file. (The open call can block on certain device nodes as reported in #1929.)
To overcome the possible TOCTOU issue between stat() and open(), we double-check device, inode after we have opened the file.
This also reverts commit 50eeef4.
The original problem could also have been fixed by passing O_PATH to open(2). However, there seems to be no way to atomically upgrade those path-only fds to real file descriptors that we can mmap or read from, so this would not helped in overcoming the TOCTOU issue.