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    Subject[PATCH 4.14 163/205] exec: load_script: dont blindly truncate shebang string
    Date
    4.14-stable review patch.  If anyone has any objections, please let me know.

    ------------------

    [ Upstream commit 8099b047ecc431518b9bb6bdbba3549bbecdc343 ]

    load_script() simply truncates bprm->buf and this is very wrong if the
    length of shebang string exceeds BINPRM_BUF_SIZE-2. This can silently
    truncate i_arg or (worse) we can execute the wrong binary if buf[2:126]
    happens to be the valid executable path.

    Change load_script() to return ENOEXEC if it can't find '\n' or zero in
    bprm->buf. Note that '\0' can come from either
    prepare_binprm()->memset() or from kernel_read(), we do not care.

    Link: http://lkml.kernel.org/r/20181112160931.GA28463@redhat.com
    Signed-off-by: Oleg Nesterov <oleg@redhat.com>
    Acked-by: Kees Cook <keescook@chromium.org>
    Acked-by: Michal Hocko <mhocko@suse.com>
    Cc: Ben Woodard <woodard@redhat.com>
    Cc: "Eric W. Biederman" <ebiederm@xmission.com>
    Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
    Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
    Signed-off-by: Sasha Levin <sashal@kernel.org>
    ---
    fs/binfmt_script.c | 10 +++++++---
    1 file changed, 7 insertions(+), 3 deletions(-)

    diff --git a/fs/binfmt_script.c b/fs/binfmt_script.c
    index 7cde3f46ad26..d0078cbb718b 100644
    --- a/fs/binfmt_script.c
    +++ b/fs/binfmt_script.c
    @@ -42,10 +42,14 @@ static int load_script(struct linux_binprm *bprm)
    fput(bprm->file);
    bprm->file = NULL;

    - bprm->buf[BINPRM_BUF_SIZE - 1] = '\0';
    - if ((cp = strchr(bprm->buf, '\n')) == NULL)
    - cp = bprm->buf+BINPRM_BUF_SIZE-1;
    + for (cp = bprm->buf+2;; cp++) {
    + if (cp >= bprm->buf + BINPRM_BUF_SIZE)
    + return -ENOEXEC;
    + if (!*cp || (*cp == '\n'))
    + break;
    + }
    *cp = '\0';
    +
    while (cp > bprm->buf) {
    cp--;
    if ((*cp == ' ') || (*cp == '\t'))
    --
    2.19.1


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