fix invalid library phdr pointers passed to callback from dl_iterate_phdr

map_library was saving pointers to an automatic-storage buffer rather
than pointers into the mapping. this should be a fairly simple fix,
but the patch here is slightly complicated by two issues:

1. supporting gratuitously obfuscated ELF files where the program
headers are not right at the beginning of the file.

2. cleaning up the map_library function so that data isn't clobbered
by the time we need it.

diff --git a/src/ldso/dynlink.c b/src/ldso/dynlink.c
index 7031d03..ff5b738 100644 (file)
--- a/src/ldso/dynlink.c
+++ b/src/ldso/dynlink.c
@@ -309,7 +309,7 @@ static void *map_library(int fd, struct dso *dso)
        size_t this_min, this_max;
        off_t off_start;
        Ehdr *eh;
-       Phdr *ph;
+       Phdr *ph, *ph0;
        unsigned prot;
        unsigned char *map, *base;
        size_t dyn;
@@ -324,11 +324,10 @@ static void *map_library(int fd, struct dso *dso)
        if (eh->e_phoff + phsize > l) {
                l = pread(fd, buf+1, phsize, eh->e_phoff);
                if (l != phsize) return 0;
-               eh->e_phoff = sizeof *eh;
+               ph = ph0 = (void *)(buf + 1);
+       } else {
+               ph = ph0 = (void *)((char *)buf + eh->e_phoff);
        }
-       ph = (void *)((char *)buf + eh->e_phoff);
-       dso->phdr = ph;
-       dso->phnum = eh->e_phnum;
        for (i=eh->e_phnum; i; i--, ph=(void *)((char *)ph+eh->e_phentsize)) {
                if (ph->p_type == PT_DYNAMIC)
                        dyn = ph->p_vaddr;
@@ -363,9 +362,18 @@ static void *map_library(int fd, struct dso *dso)
        map = mmap((void *)addr_min, map_len, prot, MAP_PRIVATE, fd, off_start);
        if (map==MAP_FAILED) return 0;
        base = map - addr_min;
-       ph = (void *)((char *)buf + eh->e_phoff);
-       for (i=eh->e_phnum; i; i--, ph=(void *)((char *)ph+eh->e_phentsize)) {
+       dso->phdr = 0;
+       dso->phnum = 0;
+       for (ph=ph0, i=eh->e_phnum; i; i--, ph=(void *)((char *)ph+eh->e_phentsize)) {
                if (ph->p_type != PT_LOAD) continue;
+               /* Check if the programs headers are in this load segment, and
+                * if so, record the address for use by dl_iterate_phdr. */
+               if (!dso->phdr && eh->e_phoff >= ph->p_offset
+                   && eh->e_phoff+phsize <= ph->p_offset+ph->p_filesz) {
+                       dso->phdr = (void *)(base + ph->p_vaddr
+                               + (eh->e_phoff-ph->p_offset));
+                       dso->phnum = eh->e_phnum;
+               }
                /* Reuse the existing mapping for the lowest-address LOAD */
                if ((ph->p_vaddr & -PAGE_SIZE) == addr_min) continue;
                this_min = ph->p_vaddr & -PAGE_SIZE;
@@ -390,8 +398,7 @@ static void *map_library(int fd, struct dso *dso)
                                goto error;
                        break;
                }
-       if (!runtime) reclaim_gaps(base, (void *)((char *)buf + eh->e_phoff),
-               eh->e_phentsize, eh->e_phnum);
+       if (!runtime) reclaim_gaps(base, ph0, eh->e_phentsize, eh->e_phnum);
        dso->map = map;
        dso->map_len = map_len;
        dso->base = base;