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fcntl.2: Note the race when O_CLOEXEC is used at same time as fork()+execve() 

Signed-off-by: Michael Kerrisk <mtk.manpages@gmail.com>
This commit is contained in:
Michael Kerrisk 2014-04-20 07:59:39 +02:00
parent 7756d15761
commit 2f4772d2d2
1 changed files with 16 additions and 1 deletions
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17
man2/fcntl.2
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@ -58,7 +58,7 @@
.\" 2010-06-17, Michael Kerrisk
.\" Document F_SETPIPE_SZ and F_GETPIPE_SZ.
.\"
.TH FCNTL 2 2014-02-20 "Linux" "Linux Programmer's Manual"
.TH FCNTL 2 2014-04-20 "Linux" "Linux Programmer's Manual"
.SH NAME
fcntl \- manipulate file descriptor
.SH SYNOPSIS
@ -142,6 +142,21 @@ is ignored.
.BR F_SETFD " (\fIint\fP)"
Set the file descriptor flags to the value specified by
.IR arg .
.PP
In multithreaded programs, using
.BR fcntl ()
.B F_SETFD
to set the close-on-exec flag at the same time as another thread performs a
.BR fork (2)
plus
.BR execve (2)
is vulnerable to a race condition that may unintentionally leak
the file descriptor to the program executed in the child process.
See the discussion of the
.BR O_CLOEXEC
flag in
.BR open (2)
for details and a remedy to the problem.
.SS File status flags
Each open file description has certain associated status flags,
initialized by