From 90d9d9ce2fbeef0f24a957efa83f5a78367a84d4 Mon Sep 17 00:00:00 2001 From: Florian Weimer Date: Mon, 25 Jun 2018 18:56:42 +0200 Subject: getgrent_next_nss (compat-initgroups): Remove alloca fallback [BZ #18023] If the caller-supplied buffer is not large enough, fall back directly malloc. The previous __libc_use_alloca check was incorrect because it did not take into account that extend_alloca may fail to merge allocations, so it would underestimate the stack space being used by roughly a factor of two. --- nss/nss_compat/compat-initgroups.c | 46 +++++++++++++++++--------------------- 1 file changed, 21 insertions(+), 25 deletions(-) (limited to 'nss') diff --git a/nss/nss_compat/compat-initgroups.c b/nss/nss_compat/compat-initgroups.c index 74414f4622..540eee863c 100644 --- a/nss/nss_compat/compat-initgroups.c +++ b/nss/nss_compat/compat-initgroups.c @@ -261,7 +261,6 @@ getgrent_next_nss (ent_t *ent, char *buffer, size_t buflen, const char *user, overwrite the pointer with one to a bigger buffer. */ char *tmpbuf = buffer; size_t tmplen = buflen; - bool use_malloc = false; for (int i = 0; i < mystart; i++) { @@ -270,29 +269,26 @@ getgrent_next_nss (ent_t *ent, char *buffer, size_t buflen, const char *user, == NSS_STATUS_TRYAGAIN && *errnop == ERANGE) { - if (__libc_use_alloca (tmplen * 2)) - { - if (tmpbuf == buffer) - { - tmplen *= 2; - tmpbuf = __alloca (tmplen); - } - else - tmpbuf = extend_alloca (tmpbuf, tmplen, tmplen * 2); - } - else - { - tmplen *= 2; - char *newbuf = realloc (use_malloc ? tmpbuf : NULL, tmplen); - - if (newbuf == NULL) - { - status = NSS_STATUS_TRYAGAIN; - goto done; - } - use_malloc = true; - tmpbuf = newbuf; - } + /* Check for overflow. */ + if (__glibc_unlikely (tmplen * 2 < tmplen)) + { + __set_errno (ENOMEM); + status = NSS_STATUS_TRYAGAIN; + goto done; + } + /* Increase the size. Make sure that we retry + with a reasonable size. */ + tmplen *= 2; + if (tmplen < 1024) + tmplen = 1024; + if (tmpbuf != buffer) + free (tmpbuf); + tmpbuf = malloc (tmplen); + if (__glibc_unlikely (tmpbuf == NULL)) + { + status = NSS_STATUS_TRYAGAIN; + goto done; + } } if (__builtin_expect (status != NSS_STATUS_NOTFOUND, 1)) @@ -320,7 +316,7 @@ getgrent_next_nss (ent_t *ent, char *buffer, size_t buflen, const char *user, status = NSS_STATUS_NOTFOUND; done: - if (use_malloc) + if (tmpbuf != buffer) free (tmpbuf); } -- cgit 1.4.1