glibc

Branch: master

Qixing ksyx Xue dbfc83bdca elf: Add test for locating libraries in root dir (bug 30435) 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. Writeup by Moody Liu <mooodyhunter@outlook.com> Suggested-by: Carlos O'Donell <carlos@redhat.com> Signed-off-by: Qixing ksyx Xue <qixingxue@outlook.com> Reviewed-by: Siddhesh Poyarekar <siddhesh@sourceware.org>	3 years ago
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preclean.req	elf: Add test for locating libraries in root dir (bug 30435)	3 years ago

Qixing ksyx Xue dbfc83bdca elf: Add test for locating libraries in root dir (bug 30435)

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.

Writeup by Moody Liu <mooodyhunter@outlook.com>

Suggested-by: Carlos O'Donell <carlos@redhat.com>
Signed-off-by: Qixing ksyx Xue <qixingxue@outlook.com>
Reviewed-by: Siddhesh Poyarekar <siddhesh@sourceware.org>

3 years ago

preclean.req

elf: Add test for locating libraries in root dir (bug 30435)

3 years ago