perf symbols: Fix use after free in filename__read_build_id

In filename__read_build_id, phdr points to memory in buf, which gets realloced
before a call to fseek that uses phdr->p_offset. This change stores the value
of p_offset before buf is realloced, so the fseek can use the value safely.

Signed-off-by: Mitchell Krome <mitchellkrome@gmail.com>
Cc: Jiri Olsa <jolsa@kernel.org>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Jiri Olsa <jolsa@redhat.com>
Cc: Paul Mackerras <paulus@samba.org>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Link: http://lkml.kernel.org/r/20141216021612.GA7199@mitchell
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>

1 files changed, 6 insertions, 2 deletions

diff --git a/tools/perf/util/symbol-minimal.c b/tools/perf/util/symbol-minimal.c
index fa585c63f56a..d7efb03b3f9a 100644
--- a/tools/perf/util/symbol-minimal.c
+++ b/tools/perf/util/symbol-minimal.c
@@ -129,6 +129,7 @@ int filename__read_build_id(const char *filename, void *bf, size_t size)
 
                 for (i = 0, phdr = buf; i < ehdr.e_phnum; i++, phdr++) {
                         void *tmp;
+                        long offset;
 
                         if (need_swap) {
                                 phdr->p_type = bswap_32(phdr->p_type);
@@ -140,12 +141,13 @@ int filename__read_build_id(const char *filename, void *bf, size_t size)
                                 continue;
 
                         buf_size = phdr->p_filesz;
+                        offset = phdr->p_offset;
                         tmp = realloc(buf, buf_size);
                         if (tmp == NULL)
                                 goto out_free;
 
                         buf = tmp;
-                        fseek(fp, phdr->p_offset, SEEK_SET);
+                        fseek(fp, offset, SEEK_SET);
                         if (fread(buf, buf_size, 1, fp) != 1)
                                 goto out_free;
 
@@ -178,6 +180,7 @@ int filename__read_build_id(const char *filename, void *bf, size_t size)
 
                 for (i = 0, phdr = buf; i < ehdr.e_phnum; i++, phdr++) {
                         void *tmp;
+                        long offset;
 
                         if (need_swap) {
                                 phdr->p_type = bswap_32(phdr->p_type);
@@ -189,12 +192,13 @@ int filename__read_build_id(const char *filename, void *bf, size_t size)
                                 continue;
 
                         buf_size = phdr->p_filesz;
+                        offset = phdr->p_offset;
                         tmp = realloc(buf, buf_size);
                         if (tmp == NULL)
                                 goto out_free;
 
                         buf = tmp;
-                        fseek(fp, phdr->p_offset, SEEK_SET);
+                        fseek(fp, offset, SEEK_SET);
                         if (fread(buf, buf_size, 1, fp) != 1)
                                 goto out_free;