From 3e90d04af98c476f024ec12e5296b88d6dd830bf Mon Sep 17 00:00:00 2001 From: Wayne Pollock Date: Wed, 4 May 2016 17:15:14 +0100 Subject: write: fix setuid related regression The write(1) is commonly a setuid binary, because common users cannot by default write to each others terminals. Since the commit in reference, that is part of releases v2.24 to v2.28, the write(1) has used access(2) to check capability to write to a destination terminal. The catch is that access(2) uses real UID and GID to when performing the accessibility. The obvious correction is to avoid access(2) when in context of setuid binaries. As a smaller fix, but equally important fix, ensure the 'msgsok' variable is initialized to indicate no access. Uninitialized variable will almost certainly do wrong thing at the time of check. Breaking-commit: 0233a8ea18bec17dd59cfe1fec8281 Signed-off-by: Sami Kerola Signed-off-by: Karel Zak Signed-off-by: Wayne Pollock --- term-utils/write.c | 14 +++++++------- 1 file changed, 7 insertions(+), 7 deletions(-) (limited to 'term-utils/write.c') diff --git a/term-utils/write.c b/term-utils/write.c index 238040be2..14594f5d9 100644 --- a/term-utils/write.c +++ b/term-utils/write.c @@ -97,7 +97,7 @@ int main(int argc, char **argv) { time_t atime; uid_t myuid; - int msgsok, myttyfd, c; + int msgsok = 0, myttyfd, c; char tty[PATH_MAX], *mytty; static const struct option longopts[] = { @@ -151,7 +151,7 @@ int main(int argc, char **argv) if (!msgsok) errx(EXIT_FAILURE, _("you have write permission turned off")); - + msgsok = 0; } else mytty = ""; @@ -230,7 +230,7 @@ void search_utmp(char *user, char *tty, char *mytty, uid_t myuid) struct utmp u; struct utmp *uptr; time_t bestatime, atime; - int nloggedttys, nttys, msgsok, user_is_me; + int nloggedttys, nttys, msgsok = 0, user_is_me; char atty[sizeof(u.ut_line) + 1]; utmpname(_PATH_UTMP); @@ -300,10 +300,10 @@ int term_chk(char *tty, int *msgsokP, time_t * atimeP, int showerror) warn("%s", path); return 1; } - - *msgsokP = !access(path, W_OK); - if (!root_access && *msgsokP) - *msgsokP = s.st_mode & S_IWGRP; + if (getuid() == 0) /* root can always write */ + *msgsokP = 1; + else + *msgsokP = (s.st_mode & S_IWGRP) && (getegid() == s.st_gid); *atimeP = s.st_atime; return 0; } -- cgit v1.2.3-55-g7522