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select.2: Strengthen the warning regarding the low value of FD_SETSIZE
All modern code should avoid select(2) in favor of poll(2) or epoll(7). For a long history of this problem, see: https://marc.info/?l=bugtraq&m=110660879328901 List: bugtraq Subject: SECURITY.NNOV: Multiple applications fd_set structure bitmap array index overflow From: 3APA3A <3APA3A () security ! nnov ! ru> Date: 2005-01-24 20:30:08 https://sourceware.org/legacy-ml/libc-alpha/2003-05/msg00171.html User-settable FD_SETSIZE and select() From: mtk-lists at gmx dot net To: libc-alpha at sources dot redhat dot com Date: Mon, 19 May 2003 14:49:03 +0200 (MEST) Subject: User-settable FD_SETSIZE and select() https://sourceware.org/bugzilla/show_bug.cgi?id=10352 http://0pointer.net/blog/file-descriptor-limits.html https://twitter.com/pid_eins/status/1394962183033868292 Signed-off-by: Michael Kerrisk <mtk.manpages@gmail.com>
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@ -70,6 +70,18 @@ Feature Test Macro Requirements for glibc (see
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_POSIX_C_SOURCE >= 200112L
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.fi
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.SH DESCRIPTION
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.BR "WARNING" :
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.BR select ()
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can monitor only file descriptors numbers that are less than
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.BR FD_SETSIZE
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(1024)\(eman unreasonably low limit for many modern applications\(emand
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this limitation will not change.
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All modern applications should instead use
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.BR poll (2)
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or
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.BR epoll (7),
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which do not suffer this limitation.
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.PP
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.BR select ()
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allows a program to monitor multiple file descriptors,
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waiting until one or more of the file descriptors become "ready"
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@ -80,15 +92,6 @@ perform a corresponding I/O operation (e.g.,
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or a sufficiently small
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.BR write (2))
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without blocking.
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.PP
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.BR select ()
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can monitor only file descriptors numbers that are less than
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.BR FD_SETSIZE ;
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.BR poll (2)
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and
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.BR epoll (7)
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do not have this limitation.
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See BUGS.
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.\"
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.SS File descriptor sets
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The principal arguments of
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