• Michael Kerrisk (man-pages)'s avatar
    pipe: cap initial pipe capacity according to pipe-max-size limit · 086e774a
    Michael Kerrisk (man-pages) authored
    This is a patch that provides behavior that is more consistent, and
    probably less surprising to users. I consider the change optional, and
    welcome opinions about whether it should be applied.
    
    By default, pipes are created with a capacity of 64 kiB.  However,
    /proc/sys/fs/pipe-max-size may be set smaller than this value.  In this
    scenario, an unprivileged user could thus create a pipe whose initial
    capacity exceeds the limit. Therefore, it seems logical to cap the
    initial pipe capacity according to the value of pipe-max-size.
    
    The test program shown earlier in this patch series can be used to
    demonstrate the effect of the change brought about with this patch:
    
        # cat /proc/sys/fs/pipe-max-size
        1048576
        # sudo -u mtk ./test_F_SETPIPE_SZ 1
        Initial pipe capacity: 65536
        # echo 10000 > /proc/sys/fs/pipe-max-size
        # cat /proc/sys/fs/pipe-max-size
        16384
        # sudo -u mtk ./test_F_SETPIPE_SZ 1
        Initial pipe capacity: 16384
        # ./test_F_SETPIPE_SZ 1
        Initial pipe capacity: 65536
    
    The last two executions of 'test_F_SETPIPE_SZ' show that pipe-max-size
    caps the initial allocation for a new pipe for unprivileged users, but
    not for privileged users.
    
    Link: http://lkml.kernel.org/r/31dc7064-2a17-9c5b-1df1-4e3012ee992c@gmail.comSigned-off-by: default avatarMichael Kerrisk <mtk.manpages@gmail.com>
    Reviewed-by: default avatarVegard Nossum <vegard.nossum@oracle.com>
    Cc: Willy Tarreau <w@1wt.eu>
    Cc: <socketpair@gmail.com>
    Cc: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>
    Cc: Jens Axboe <axboe@fb.com>
    Cc: Al Viro <viro@zeniv.linux.org.uk>
    Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
    Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
    086e774a
pipe.c 27.3 KB