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On 2017-12-17 23:07, Dmitry V. Levin wrote: > On Sun, Dec 17, 2017 at 06:21:49PM +0100, Aurelien Jarno wrote: > > The fillin_rpath function in elf/dl-load.c loops over each RPATH or > > RUNPATH tokens and intepret empty tokens as the current directory > > ("./"). In practice the check for empty token is done *after* the > > dynamic string token expansion. The expansion process can return an > > empty string for the $ORIGIN token if __libc_enable_secure is set > > or if the path of the binary can not be determined (/proc not mounted). > > > > Fix that by moving the check for empty tokens before the dynamic string > > token expansion. In addition, check for NULL pointer or empty strings > > return by expand_dynamic_string_token. > > > > The above changed highlighted a bug in decompose_rpath, an empty array > > is represented by the first element being NULL at the fillin_rpath path > > level, but by using a -1 pointer in decompose_rpath and other functions. > > > > Changelog: > > [BZ #22625] > > * elf/dl-load.c (fillin_rpath): Check for empty tokens before > > dynamic string token expansion. Check for NULL pointer or empty > > string possibly returned by expand_dynamic_string_token. > > (decompose_rpath): Check for empty path after dynamic string > > token expansion. > > Accidentally, I was looking at this issue recently and have been testing > a slightly different patch, so I'd just share my thoughts. > > > --- > > ChangeLog | 9 +++++++++ > > NEWS | 4 ++++ > > elf/dl-load.c | 30 ++++++++++++++++++++++++++---- > > 3 files changed, 39 insertions(+), 4 deletions(-) > > > > diff --git a/ChangeLog b/ChangeLog > > index 815e73571d..4ef438d08c 100644 > > --- a/ChangeLog > > +++ b/ChangeLog > > @@ -1,3 +1,12 @@ > > +2017-12-17 Aurelien Jarno <aurelien@aurel32.net> > > + > > + [BZ #22625] > > + * elf/dl-load.c (fillin_rpath): Check for empty tokens before > > + dynamic string token expansion. Check for NULL pointer or empty > > + string possibly returned by expand_dynamic_string_token. > > + (decompose_rpath): Check for empty path after dynamic string > > + token expansion. > > + > > 2017-12-16 Aurelien Jarno <aurelien@aurel32.net> > > > > [BZ #22505] > > diff --git a/NEWS b/NEWS > > index 0670585b4c..8099ecc8f1 100644 > > --- a/NEWS > > +++ b/NEWS > > @@ -149,6 +149,10 @@ Security related changes: > > CVE-2017-1000366 has been applied, but it is mentioned here only because > > of the CVE assignment.) Reported by Qualys. > > > > + CVE-2017-16997: Incorrect handling of RPATH or RUNPATH containing $ORIGIN > > + for AT_SECURE or SUID binaries could be used to load libraries from the > > + current directory. > > + > > The following bugs are resolved with this release: > > > > [The release manager will add the list generated by > > diff --git a/elf/dl-load.c b/elf/dl-load.c > > index bbd3be9e20..81a1a03a01 100644 > > --- a/elf/dl-load.c > > +++ b/elf/dl-load.c > > @@ -433,14 +433,11 @@ fillin_rpath (char *rpath, struct r_search_path_elem **result, const char *sep, > > { > > char *cp; > > size_t nelems = 0; > > - char *to_free; > > + char *to_free = NULL; > > Let's use this opportunity and move to_free inside the loop. Indeed. I was even wondering if we can just use cp = strdup("./") below to get rid of to_free and limit the amount of different code paths. > > while ((cp = __strsep (&rpath, sep)) != NULL) > > { > > struct r_search_path_elem *dirp; > > - > > - to_free = cp = expand_dynamic_string_token (l, cp, 1); > > - > > size_t len = strlen (cp); > > > > /* `strsep' can pass an empty string. This has to be > > I think the code would be easier to read if len == 0 check below was > changed to *cp == '\0'. This way you wouldn't have to call strlen twice, > and ... > > > @@ -450,6 +447,24 @@ fillin_rpath (char *rpath, struct r_search_path_elem **result, const char *sep, > > static const char curwd[] = "./"; > > cp = (char *) curwd; > > ... an explicit len = 0 assignment would highlight the nastiness > of the trick with len later in fillin_rpath. Good idea indeed. > > } > > + else > > + { > > + to_free = cp = expand_dynamic_string_token (l, cp, 1); > > + > > + /* expand_dynamic_string_token can return NULL in case of memory > > + allocation failure. */ > > + if (cp == NULL) > > + continue; > > + > > + /* Recompute the length after dynamic string token expansion > > + and ignore empty paths. */ > > + len = strlen (cp); > > + if (len == 0) > > + { > > + free (to_free); > > + continue; > > + } > > + } > > The alternative (that I was testing in my patch) to len == 0 check is to > change expand_dynamic_string_token to return NULL if _dl_dst_substitute > returned an empty string, e.g. > > - return _dl_dst_substitute (l, s, result, is_path); > + char *retval = _dl_dst_substitute (l, s, result, is_path); > + > + /* If substitution of dynamic string tokens resulted to an empty string, > + return NULL as in case of insufficient memory. */ > + if (__glibc_unlikely (*retval == '\0')) > + { > + free (result); > + return NULL; > + } > + > + return retval; > > Both users of expand_dynamic_string_token, fillin_rpath and _dl_map_object, > would be happy. I thought about that, but refrained as much as possible to change any interface, as it might trigger more bugs, even if it looks ok. The current bug actually show that a simple change might have big consequences. Overall it seems the RPATH handling code became very complex over the time, and would clearly benefit from a rewrite. I would not be really surprised if other similar bugs are found. All that said, if a few more persons review that code path, that should be fine. > > /* Remove trailing slashes (except for "/"). */ > > while (len > 1 && cp[len - 1] == '/') > > @@ -620,6 +635,13 @@ decompose_rpath (struct r_search_path_struct *sps, > > necessary. */ > > free (copy); > > > > + /* There is no path after expansion. */ > > + if (result[0] == NULL) { > > + free (result); > > + sps->dirs = (struct r_search_path_elem **) -1; > > + return false; > > + } > > + > > sps->dirs = result; > > /* The caller will change this value if we haven't used a real malloc. */ > > sps->malloced = 1; > > Yes, the bug was just sitting here and waiting for a fix in fillin_rpath > to explode. Yes, however there is at least one more "continue" in fillin_rpath which can lead to an empty path after expansion. I am surprised it didn't trigger before today. Thanks for the review! -- Aurelien Jarno GPG: 4096R/1DDD8C9B aurelien@aurel32.net http://www.aurel32.net
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