[PATCH] perf tool: Fix use after free in filename__read_build_id

[PATCH] perf tool: Fix use after free in filename__read_build_id

[Mitchell Krome]

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>
---
 tools/perf/util/symbol-minimal.c | 8 ++++++--
 1 file changed, 6 insertions(+), 2 deletions(-)

diff --git a/tools/perf/util/symbol-minimal.c b/tools/perf/util/symbol-minimal.c
index fa585c6..d7efb03 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;
 
-- 
1.9.1

Re: [PATCH] perf tool: Fix use after free in filename__read_build_id

[Jiri Olsa]

On Tue, Dec 16, 2014 at 12:16:12PM +1000, Mitchell Krome wrote:
> 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>
> ---
>  tools/perf/util/symbol-minimal.c | 8 ++++++--
>  1 file changed, 6 insertions(+), 2 deletions(-)
> 
> diff --git a/tools/perf/util/symbol-minimal.c b/tools/perf/util/symbol-minimal.c
> index fa585c6..d7efb03 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);

so the concern is that the realloc buf_size will be smaller
than the 'buf' offset of phdr->p_offset value, right? Anyway:

Acked-by: Jiri Olsa <jolsa@kernel.org>

jirka

Re: [PATCH] perf tool: Fix use after free in filename__read_build_id

[Arnaldo Carvalho de Melo]

Em Tue, Dec 16, 2014 at 04:35:23PM +0100, Jiri Olsa escreveu:
> On Tue, Dec 16, 2014 at 12:16:12PM +1000, Mitchell Krome wrote:
> > 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>
> > ---
> >  tools/perf/util/symbol-minimal.c | 8 ++++++--
> >  1 file changed, 6 insertions(+), 2 deletions(-)
> > 
> > diff --git a/tools/perf/util/symbol-minimal.c b/tools/perf/util/symbol-minimal.c
> > index fa585c6..d7efb03 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);
> 
> so the concern is that the realloc buf_size will be smaller
> than the 'buf' offset of phdr->p_offset value, right? Anyway:

at first I got unsure because of what realloc man page says, i.e. the
common part will have the same contents, i.e. before and after what is
in a a given offset will remain the same if in an area <= new size.

But yeah, if phdr->p_filesz < offsetof(Elf32_Phdr, p_offset) (unlikely,
I guess), then accessing phdr->p_offset after the realloc may be unsafe
(perhaps when using some off-limits memory access tool that paints freed
memory?).

Anyway, the new code is clear and more robust, applying.
 
> Acked-by: Jiri Olsa <jolsa@kernel.org>

Thanks,

> jirka

[tip:perf/urgent] perf symbols: Fix use after free in filename__read_build_id

[tip-bot for Mitchell Krome]

Commit-ID:  7ad74b41e56e4f7f42c6b765bc44428cd09310d7
Gitweb:     http://git.kernel.org/tip/7ad74b41e56e4f7f42c6b765bc44428cd09310d7
Author:     Mitchell Krome <mitchellkrome@gmail.com>
AuthorDate: Tue, 16 Dec 2014 12:16:12 +1000
Committer:  Arnaldo Carvalho de Melo <acme@redhat.com>
CommitDate: Wed, 17 Dec 2014 11:58:17 -0300

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>
---
 tools/perf/util/symbol-minimal.c | 8 ++++++--
 1 file changed, 6 insertions(+), 2 deletions(-)

diff --git a/tools/perf/util/symbol-minimal.c b/tools/perf/util/symbol-minimal.c
index fa585c6..d7efb03 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;