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Bug #78987 Memory problems running finfo::buffer with PHP_CLI
Submitted: 2019-12-18 04:12 UTC Modified: 2019-12-18 10:58 UTC
Avg. Score:4.2 ± 0.9
Reproduced:5 of 5 (100.0%)
Same Version:2 (40.0%)
Same OS:2 (40.0%)
From: jhhillie at amazon dot com Assigned:
Status: Verified Package: Filesystem function related
PHP Version: 7.4Git-2019-12-18 (Git) OS: Ubuntu
Private report: No CVE-ID: None
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 [2019-12-18 04:12 UTC] jhhillie at amazon dot com
When calling finfo::buffer() with a crafted string, PHP tries to allocate an insane amount of memory to do so. I found a similar bug here -

I suspect the bug may have been re-introduced at some stage during newer versions.

1) I tested it on the version my customer had been using - v7.0.33 (doesn't work)
2) I then tested on the latest php version - v7.4.0 (doesn't work)
3) Testing on an older version - v5.4.16 it works perfectly.

Test script:
Generated a random file of 300MB using:
      $ sudo fallocate -l 300M test-file

The script used:

	$content = file_get_contents('test-file', true);
	$fileInfo = new \finfo(FILEINFO_MIME_TYPE);

Expected result:
To provide the file metadata (I know there are other ways to do this):

string(19) "application/x-empty"

Actual result:
PHP Warning:  finfo::buffer(): Failed identify data 12:cannot allocate 2516582408 bytes (Cannot allocate memory)application/octet-stream in php shell code on line 1 bool(false)


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 [2019-12-18 04:51 UTC]
-Status: Open +Status: Feedback -Package: Performance problem +Package: Filesystem function related
 [2019-12-18 04:51 UTC]
> Failed identify data 12:cannot allocate 2516582408 bytes (Cannot allocate memory)application/octet-stream
According to that, libmagic is the one failing.

Working for me with PHP 7.0-7.4 on Ubuntu.

Does it actually include "application/octet-stream" in there? That is the correct MIME type...
I assume the system is, in fact, running out of memory? What version of libmagic?
 [2019-12-18 10:58 UTC]
-Status: Feedback +Status: Verified
 [2019-12-18 10:58 UTC]
I can reproduce the large allocation. It is caused by

Basically, libmagic tries to detect the encoding of the file and does this by ... allocating a buffer of unicode characters for the whole file.

For some reason this also uses "unsigned long" instead of "uint32_t" for each character, which means the allocation is not just 4 times as large, but 8 times as large as the original file!

Current upstream version still looks about the same:

Ideally this issue would be reported upstream and fixed there first.
 [2020-06-12 07:12 UTC] magnar at myrtveit dot com
I've created two scripts that illustrate the problem with finfo_buffer:

Memory usage of finfo_file:
Memory usage of finfo_buffer:

On a 16M file, finfo_file uses 20M memory. finfo_buffer, however, uses 244M!
 [2021-01-09 07:26 UTC] sydneymylee62 at gmail dot com
Thanks for the update and quick reply. I'll be sure to keep an eye on this thread.    Looking for the same issue. Bumped into your thread. Thanks for creating it. Looking forward for solution.
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