| Message ID | 20190206194529.24952-1-plautrba@redhat.com (mailing list archive) |
|---|---|
| State | Superseded |
| Headers | show |
| Series | libsemanage: genhomedircon - improve handling large groups | expand |
On Wed, Feb 6, 2019 at 8:45 PM Petr Lautrbach <plautrba@redhat.com> wrote: > > 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> > --- > libsemanage/src/genhomedircon.c | 16 +++++++++++++--- > 1 file changed, 13 insertions(+), 3 deletions(-) > > diff --git a/libsemanage/src/genhomedircon.c b/libsemanage/src/genhomedircon.c > index 591941fb..ac376671 100644 > --- a/libsemanage/src/genhomedircon.c > +++ b/libsemanage/src/genhomedircon.c > @@ -1077,10 +1077,20 @@ 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; > + new_grbuf = realloc(grbuf, grbuflen); > + if (new_grbuf == NULL) > + goto cleanup; > + grbuf = new_grbuf; > } Hello, When reading this for loop, I am concerned about the case where the member list exceeds 2Go on a system with a 32-bit CPU (where sizeof(long) = 4). Even if it seems very unlikely, if this ever happens, the loop will become infinite. Would you agree with adding "&& grbuflen > 0" to the condition of the while statement? Anyway, if you do not agree, this patch looks good to me. Acked-by: Nicolas Iooss <nicolas.iooss@m4x.org> Thanks, Nicolas > + if (retval == -1) > + goto cleanup; > > if (group == NULL) { > ERR(s->h_semanage, "Can't find group named %s\n", grname); > -- > 2.20.1 >
Nicolas Iooss <nicolas.iooss@m4x.org> writes: > On Wed, Feb 6, 2019 at 8:45 PM Petr Lautrbach > <plautrba@redhat.com> wrote: >> >> 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> >> --- >> libsemanage/src/genhomedircon.c | 16 +++++++++++++--- >> 1 file changed, 13 insertions(+), 3 deletions(-) >> >> diff --git a/libsemanage/src/genhomedircon.c >> b/libsemanage/src/genhomedircon.c >> index 591941fb..ac376671 100644 >> --- a/libsemanage/src/genhomedircon.c >> +++ b/libsemanage/src/genhomedircon.c >> @@ -1077,10 +1077,20 @@ 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; >> + new_grbuf = realloc(grbuf, grbuflen); >> + if (new_grbuf == NULL) >> + goto cleanup; >> + grbuf = new_grbuf; >> } > > Hello, > When reading this for loop, I am concerned about the case where > the > member list exceeds 2Go on a system with a 32-bit CPU (where > sizeof(long) = 4). Even if it seems very unlikely, if this ever > happens, the loop will become infinite. Would you agree with > adding > "&& grbuflen > 0" to the condition of the while statement? Makes sense, I'll add it. Thanks. > Anyway, if you do not agree, this patch looks good to me. > Acked-by: Nicolas Iooss <nicolas.iooss@m4x.org> > > Thanks, > Nicolas > >> + if (retval == -1) >> + goto cleanup; According to the man page this check is not correct. - "In case of error, an error number is returned, and NULL is stored in *result." I'll fix it as well. >> if (group == NULL) { >> ERR(s->h_semanage, "Can't find group named >> %s\n", grname); >> -- >> 2.20.1 >>
diff --git a/libsemanage/src/genhomedircon.c b/libsemanage/src/genhomedircon.c index 591941fb..ac376671 100644 --- a/libsemanage/src/genhomedircon.c +++ b/libsemanage/src/genhomedircon.c @@ -1077,10 +1077,20 @@ 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; + new_grbuf = realloc(grbuf, grbuflen); + if (new_grbuf == NULL) + goto cleanup; + grbuf = new_grbuf; } + if (retval == -1) + goto cleanup; if (group == NULL) { ERR(s->h_semanage, "Can't find group named %s\n", grname);
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> --- libsemanage/src/genhomedircon.c | 16 +++++++++++++--- 1 file changed, 13 insertions(+), 3 deletions(-)