From 03d2730b44cc2236318fd978afa2651753666c55 Mon Sep 17 00:00:00 2001 From: Florian Weimer Date: Wed, 29 Apr 2015 14:41:25 +0200 Subject: CVE-2014-8121: Do not close NSS files database during iteration [BZ #18007] MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit Robin Hack discovered Samba would enter an infinite loop processing certain quota-related requests. We eventually tracked this down to a glibc issue. Running a (simplified) test case under strace shows that /etc/passwd is continuously opened and closed: … open("/etc/passwd", O_RDONLY|O_CLOEXEC) = 3 lseek(3, 0, SEEK_CUR) = 0 read(3, "root:x:0:0:root:/root:/bin/bash\n"..., 4096) = 2717 lseek(3, 2717, SEEK_SET) = 2717 close(3) = 0 open("/etc/passwd", O_RDONLY|O_CLOEXEC) = 3 lseek(3, 0, SEEK_CUR) = 0 lseek(3, 0, SEEK_SET) = 0 read(3, "root:x:0:0:root:/root:/bin/bash\n"..., 4096) = 2717 lseek(3, 2717, SEEK_SET) = 2717 close(3) = 0 open("/etc/passwd", O_RDONLY|O_CLOEXEC) = 3 lseek(3, 0, SEEK_CUR) = 0 … The lookup function implementation in nss/nss_files/files-XXX.c:DB_LOOKUP has code to prevent that. It is supposed skip closing the input file if it was already open. /* Reset file pointer to beginning or open file. */ \ status = internal_setent (keep_stream); \ \ if (status == NSS_STATUS_SUCCESS) \ { \ /* Tell getent function that we have repositioned the file pointer. */ \ last_use = getby; \ \ while ((status = internal_getent (result, buffer, buflen, errnop \ H_ERRNO_ARG EXTRA_ARGS_VALUE)) \ == NSS_STATUS_SUCCESS) \ { break_if_match } \ \ if (! keep_stream) \ internal_endent (); \ } \ keep_stream is initialized from the stayopen flag in internal_setent. internal_setent is called from the set*ent implementation as: status = internal_setent (stayopen); However, for non-host database, this flag is always 0, per the STAYOPEN magic in nss/getXXent_r.c. Thus, the fix is this: - status = internal_setent (stayopen); + status = internal_setent (1); This is not a behavioral change even for the hosts database (where the application can specify the stayopen flag) because with a call to sethostent(0), the file handle is still not closed in the implementation of gethostent. --- nss/nss_files/files-XXX.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) (limited to 'nss/nss_files/files-XXX.c') diff --git a/nss/nss_files/files-XXX.c b/nss/nss_files/files-XXX.c index a7a45e5b0e..a7ce5ea97e 100644 --- a/nss/nss_files/files-XXX.c +++ b/nss/nss_files/files-XXX.c @@ -134,7 +134,7 @@ CONCAT(_nss_files_set,ENTNAME) (int stayopen) __libc_lock_lock (lock); - status = internal_setent (stayopen); + status = internal_setent (1); if (status == NSS_STATUS_SUCCESS && fgetpos (stream, &position) < 0) { -- cgit v1.2.3