[PATCH] libdw: Make sure id_path can contain max number of build id bytes.

[PATCH] libdw: Make sure id_path can contain max number of build id bytes.

[Mark Wielaard]

The MAX_BUILD_ID_BYTES is fairly large (64), while normally build-ids
are only 20 bytes long. But if we would encounter a jumbo build-id we
should have enough room to construct the full build-id path.

We used to substract 2 bytes from the max, because 2 chars are used
as subdir. But that should be 1 (2 hex chars is just one 8 bit byte).

Signed-off-by: Mark Wielaard <mark@klomp.org>
---
 libdw/ChangeLog      | 5 +++++
 libdw/dwarf_getalt.c | 2 +-
 2 files changed, 6 insertions(+), 1 deletion(-)

diff --git a/libdw/ChangeLog b/libdw/ChangeLog
index 17acb90..b9f177d 100644
--- a/libdw/ChangeLog
+++ b/libdw/ChangeLog
@@ -1,3 +1,8 @@
+2018-06-05  Mark Wielaard  <mark@klomp.org>
+
+	* dwarf_getalt.c (find_debug_altlink): id_path array should be 2
+	larger to contain MAX_BUILD_ID_BYTES.
+
 2018-05-31  Mark Wielaard  <mark@klomp.org>
 
 	* libdw_find_split_unit.c (try_split_file): New function extracted
diff --git a/libdw/dwarf_getalt.c b/libdw/dwarf_getalt.c
index 3339b3e..0a12dfa 100644
--- a/libdw/dwarf_getalt.c
+++ b/libdw/dwarf_getalt.c
@@ -123,7 +123,7 @@ find_debug_altlink (Dwarf *dbg)
     {
       /* Note sizeof a string literal includes the trailing zero.  */
       char id_path[sizeof DEBUGINFO_PATH - 1 + sizeof "/.build-id/" - 1
-		   + 2 + 1 + (MAX_BUILD_ID_BYTES - 2) * 2 + sizeof ".debug"];
+		   + 2 + 1 + (MAX_BUILD_ID_BYTES - 1) * 2 + sizeof ".debug"];
       sprintf (&id_path[0], "%s%s", DEBUGINFO_PATH, "/.build-id/");
       sprintf (&id_path[sizeof DEBUGINFO_PATH - 1 + sizeof "/.build-id/" - 1],
 	       "%02" PRIx8 "/", (uint8_t) id[0]);
-- 
1.8.3.1

Re: [PATCH] libdw: Make sure id_path can contain max number of build id bytes.

[Mark Wielaard]

On Tue, 2018-06-05 at 21:33 +0200, Mark Wielaard wrote:
> The MAX_BUILD_ID_BYTES is fairly large (64), while normally build-ids
> are only 20 bytes long. But if we would encounter a jumbo build-id we
> should have enough room to construct the full build-id path.
> 
> We used to substract 2 bytes from the max, because 2 chars are used
> as subdir. But that should be 1 (2 hex chars is just one 8 bit byte).

Pushed to master.