diff mbox series

[v2,1/2] elf: Fix marking root dir as nonexist in open_path (bug 30435)

Message ID ME2P282MB2242FEA05E8B873F6CFA60D7B4769@ME2P282MB2242.AUSP282.PROD.OUTLOOK.COM
State Superseded
Delegated to: Carlos O'Donell
Headers
Series [v2,1/2] elf: Fix marking root dir as nonexist in open_path (bug 30435) |

Commit Message

Qixing ksyx Xue May 9, 2023, 10:56 p.m. UTC 
  From: Moody Liu <mooodyhunter@outlook.com>

When dlopen is being called, efforts have been made to improve
future lookup performance. This includes marking a search path
as non-existent using `stat`. However, if the root directory
is given as a search path, there exists a bug which erroneously
marks it as non-existing.

The bug is reproduced under the following sequence:

  1. dlopen is called to open a shared library, with at least:
     1) a dependency 'A.so' not directly under the '/' directory
        (e.g. /lib/A.so), and
     2) another dependency 'B.so' resides in '/'.
  2. for this bug to reproduce, 'A.so' should be searched *before* 'B.so'.
  3. it first tries to find 'A.so' in /, (e.g. /A.so):
     - this will (obviously) fail,
     - since it's the first time we have seen the '/' directory,
       its 'status' is 'unknown'.
  4. `buf[buflen - namelen - 1] = '\0'` is executed:
     - it intends to remove the leaf and its final slash,
     - because of the speciality of '/', its buflen == namelen + 1,
     - it erroneously clears the entire buffer.
  6. it then calls 'stat' with the empty buffer:
     - which will result in an error.
  7. so it marks '/' as 'nonexisting', future lookups will not consider
     this path.
  8. while /B.so *does* exist, failure to look it up in the '/'
     directory leads to a 'cannot open shared object file' error.

This patch fixes the bug by preventing 'buflen', an index to put '\0',
from being set to 0, so that the root '/' is always kept.
Relative search paths are always considered as 'existing' so this
wont be affected.

Suggested-by: Qixing ksyx Xue <qixingxue@outlook.com>
---
 elf/dl-load.c | 6 +++++-
 1 file changed, 5 insertions(+), 1 deletion(-)
diff mbox series

Patch

diff --git a/elf/dl-load.c b/elf/dl-load.c
index 9a0e40c0e9..36cf635c03 100644
--- a/elf/dl-load.c
+++ b/elf/dl-load.c
@@ -1855,7 +1855,11 @@  open_path (const char *name, size_t namelen, int mode,
 		     test whether there is any directory at all.  */
 		  struct __stat64_t64 st;
 
-		  buf[buflen - namelen - 1] = '\0';
+		  /* We only have absolute paths go into this branch.
+		     In the rare case where 'this_dir' is only a '/', we
+		     must keep it.  */
+		  buflen = MAX(buflen - namelen - 1, 1);
+		  buf[buflen] = '\0';
 
 		  if (__stat64_time64 (buf, &st) != 0
 		      || ! S_ISDIR (st.st_mode))