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Kees Cook
591a22c14d
Commitbfb819ea20("proc: Check /proc/$pid/attr/ writes against file opener") tried to make sure that there could not be a confusion between the opener of a /proc/$pid/attr/ file and the writer. It used struct cred to make sure the privileges didn't change. However, there were existing cases where a more privileged thread was passing the opened fd to a differently privileged thread (during container setup). Instead, use mm_struct to track whether the opener and writer are still the same process. (This is what several other proc files already do, though for different reasons.) Reported-by: Christian Brauner <[email protected]> Reported-by: Andrea Righi <[email protected]> Tested-by: Andrea Righi <[email protected]> Fixes:bfb819ea20("proc: Check /proc/$pid/attr/ writes against file opener") Cc: [email protected] Signed-off-by: Kees Cook <[email protected]> Signed-off-by: Linus Torvalds <[email protected]>