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* [PATCH] elf: Fix marking root dir as nonexist in open_path
@ 2023-05-08 15:45 Moody Liu
  2023-05-08 20:04 ` Carlos O'Donell
                   ` (2 more replies)
  0 siblings, 3 replies; 9+ messages in thread
From: Moody Liu @ 2023-05-08 15:45 UTC (permalink / raw)
  To: libc-alpha; +Cc: Moody Liu, Qixing ksyx Xue

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 --git a/elf/dl-load.c b/elf/dl-load.c
index fcb39a78d4..10757dd5a5 100644
--- a/elf/dl-load.c
+++ b/elf/dl-load.c
@@ -1865,7 +1865,11 @@ 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))
-- 
2.40.1


^ permalink raw reply	[flat|nested] 9+ messages in thread
end of thread, other threads:[~2023-05-25 15:12 UTC | newest]

Thread overview: 9+ messages (download: mbox.gz / follow: Atom feed)
-- links below jump to the message on this page --
2023-05-08 15:45 [PATCH] elf: Fix marking root dir as nonexist in open_path Moody Liu
2023-05-08 20:04 ` Carlos O'Donell
2023-05-09 22:56 ` [PATCH v2 1/2] elf: Fix marking root dir as nonexist in open_path (bug 30435) Qixing ksyx Xue
2023-05-09 22:56 ` [PATCH v2 2/2] elf: Add test for finding libraries in root dir Qixing ksyx Xue
2023-05-25 12:51   ` Siddhesh Poyarekar
2023-05-25 13:29     ` [PATCH v3] elf: Add test for locating libraries in root dir (bug 30435) Qixing ksyx Xue
2023-05-25 14:52       ` Siddhesh Poyarekar
2023-05-25 14:56         ` Qixing ksyx Xue
2023-05-25 15:12           ` Siddhesh Poyarekar

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