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libsemanage: genhomedircon - improve handling large groups

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getgrnam_r() uses a preallocated buffer to store a structure containing
the broken-out fields of the record in the group database. The size of
this buffer is usually sysconf(_SC_GETGR_R_SIZE_MAX) == 1024 and it is
not enough for groups with a large number of users.  In these cases,
getgrnam_r() returns -1 and sets errno to ERANGE and the caller can
retry with a larger buffer.

Fixes:
$ semanage login -a -s user_u -r s0-s0:c1.c2 '%largegroup'
libsemanage.semanage_direct_commit: semanage_genhomedircon returned error code -1. (Numerical result out of range).
OSError: Numerical result out of range

Signed-off-by: Petr Lautrbach <plautrba@redhat.com>
This commit is contained in:
Petr Lautrbach 2019-02-06 20:45:29 +01:00
parent 913613da66
commit ffc59f6015
1 changed files with 17 additions and 3 deletions
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20
libsemanage/src/genhomedircon.c
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@ -1077,10 +1077,24 @@ static int get_group_users(genhomedircon_settings_t * s,
const char *grname = selogin + 1;
if (getgrnam_r(grname, &grstorage, grbuf,
(size_t) grbuflen, &group) != 0) {
goto cleanup;
errno = 0;
while (
(retval = getgrnam_r(grname, &grstorage, grbuf, (size_t) grbuflen, &group)) != 0 &&
errno == ERANGE
) {
char *new_grbuf;
grbuflen *= 2;
if (grbuflen < 0)
/* the member list could exceed 2Gb on a system with a 32-bit CPU (where
* sizeof(long) = 4) - if this ever happened, the loop would become infinite. */
goto cleanup;
new_grbuf = realloc(grbuf, grbuflen);
if (new_grbuf == NULL)
goto cleanup;
grbuf = new_grbuf;
}
if (retval != 0)
goto cleanup;
if (group == NULL) {
ERR(s->h_semanage, "Can't find group named %s\n", grname);