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[2016-06-25 22:19 UTC] fernando at null-life dot com
Description: ------------ imagecropauto on IMG_CROP_THRESHOLD mode causes arbitrary read access and possible leak of information. The function imagecropauto doesn't check valid colors for non-truecolor images. This causes that gdImageRed/Green/Blue/Alpha macros read beyond that 255 allowed values, when it troes match colors inside the gdColorMatch function. I'm attaching a possible patch based on the verification that was present in another PHP/gd function but this verification could also be done inside gdImageCropThreshold. Source code: https://github.com/php/php-src/blob/master/ext/gd/gd.c#L4591 color is only checked to be positive: PHP_FUNCTION(imagecropauto) { ... case GD_CROP_THRESHOLD: if (color < 0) { php_error_docref(NULL, E_WARNING, "Color argument missing with threshold mode"); RETURN_FALSE; } im_crop = gdImageCropThreshold(im, color, (float) threshold); break; ... color is passed to gdColorMatch: https://github.com/php/php-src/blob/master/ext/gd/libgd/gd_crop.c#L227 gdImagePtr gdImageCropThreshold(gdImagePtr im, const unsigned int color, const float threshold) { ... match = 1; for (y = 0; match && y < height; y++) { for (x = 0; match && x < width; x++) { match = (gdColorMatch(im, color, gdImageGetPixel(im, x,y), threshold)) > 0; } } ... https://github.com/php/php-src/blob/master/ext/gd/libgd/gd_crop.c#L344 col1 (color) is now used with the gdImageRed/gdImageGreen/gdImageBlue/gdImageAlpha macros. static int gdColorMatch(gdImagePtr im, int col1, int col2, float threshold) { const int dr = gdImageRed(im, col1) - gdImageRed(im, col2); const int dg = gdImageGreen(im, col1) - gdImageGreen(im, col2); const int db = gdImageBlue(im, col1) - gdImageBlue(im, col2); const int da = gdImageAlpha(im, col1) - gdImageAlpha(im, col2); const double dist = sqrt(dr * dr + dg * dg + db * db + da * da); const double dist_perc = sqrt(dist / (255^2 + 255^2 + 255^2)); return (dist_perc <= threshold); //return (100.0 * dist / 195075) < threshold; } In this macros it is used as an index (c) for the red/green/blue/alpha arrays, we are able to read beyond the 255 items on these arrays. https://github.com/php/php-src/blob/master/ext/gd/libgd/gd.h#L730 #define gdImageColorsTotal(im) ((im)->colorsTotal) #define gdImageRed(im, c) ((im)->trueColor ? gdTrueColorGetRed(c) : \ (im)->red[(c)]) #define gdImageGreen(im, c) ((im)->trueColor ? gdTrueColorGetGreen(c) : \ (im)->green[(c)]) #define gdImageBlue(im, c) ((im)->trueColor ? gdTrueColorGetBlue(c) : \ (im)->blue[(c)]) #define gdImageAlpha(im, c) ((im)->trueColor ? gdTrueColorGetAlpha(c) : \ (im)->alpha[(c)]) ------ ----------------------------------------------------- GDB output: gdb -q --args /home/user/php/php-70/sapi/cli/php -n poc.php No symbol table is loaded. Use the "file" command. Breakpoint 1 (__asan_report_error) pending. Reading symbols from /home/user/php/php-70/sapi/cli/php...done. gdb-peda$ b gd_crop.c:350 Breakpoint 2 at 0x8190002: file /home/user/php/php-70/ext/gd/libgd/gd_crop.c, line 350. gdb-peda$ r Starting program: /home/user/php/php-70/sapi/cli/php -n poc.php [----------------------------------registers-----------------------------------] EAX: 0x0 EBX: 0x8b47000 --> 0x8b46db8 --> 0x1 ECX: 0x60c EDX: 0x0 ESI: 0xf5a14020 --> 0xf5a7a118 --> 0x84b92de (<ZEND_DO_ICALL_SPEC_HANDLER>: push ebp) EDI: 0xf5a7a118 --> 0x84b92de (<ZEND_DO_ICALL_SPEC_HANDLER>: push ebp) EBP: 0xffff9f18 --> 0xffff9f78 --> 0xffff9fd8 --> 0xffffa008 --> 0xffffa028 --> 0xffffa068 (--> ...) ESP: 0xffff9ee0 --> 0x4 EIP: 0x8190002 (<gdColorMatch+366>: mov eax,DWORD PTR [ebp-0x28]) EFLAGS: 0x246 (carry PARITY adjust ZERO sign trap INTERRUPT direction overflow) [-------------------------------------code-------------------------------------] 0x818fffb <gdColorMatch+359>: sub edx,eax 0x818fffd <gdColorMatch+361>: mov eax,edx 0x818ffff <gdColorMatch+363>: mov DWORD PTR [ebp-0x1c],eax => 0x8190002 <gdColorMatch+366>: mov eax,DWORD PTR [ebp-0x28] 0x8190005 <gdColorMatch+369>: imul eax,DWORD PTR [ebp-0x28] 0x8190009 <gdColorMatch+373>: mov edx,eax 0x819000b <gdColorMatch+375>: mov eax,DWORD PTR [ebp-0x24] 0x819000e <gdColorMatch+378>: imul eax,DWORD PTR [ebp-0x24] [------------------------------------stack-------------------------------------] 0000| 0xffff9ee0 --> 0x4 0004| 0xffff9ee4 --> 0x1 0008| 0xffff9ee8 --> 0x4 0012| 0xffff9eec --> 0x0 0016| 0xffff9ef0 --> 0x0 0020| 0xffff9ef4 --> 0x0 0024| 0xffff9ef8 --> 0x0 0028| 0xffff9efc --> 0x0 [------------------------------------------------------------------------------] Legend: code, data, rodata, value Breakpoint 2, gdColorMatch (im=0xf5a6c000, col1=0x539, col2=0x0, threshold=0) at /home/user/php/php-70/ext/gd/libgd/gd_crop.c:350 350 const double dist = sqrt(dr * dr + dg * dg + db * db + da * da); gdb-peda$ p/d col1 $1 = 1337 gdb-peda$ p &im->red $4 = (int (*)[256]) 0xf5a6c010 ## im->red bottom limit gdb-peda$ p &im->red[255] $6 = (int *) 0xf5a6c40c ## im->red top limit gdb-peda$ p &im->red[col1] $3 = (int *) 0xf5a6d4f4 ## Out of bounds Test script: --------------- <?php $img = imagecreate(10,10); imagecropauto($img, IMG_CROP_THRESHOLD, 0, 1337); Expected result: ---------------- No crash Actual result: -------------- ASan ouput: ================================================================= ==23837==ERROR: AddressSanitizer: heap-buffer-overflow on address 0xf0d05df4 at pc 0x08681a2e bp 0xff8da798 sp 0xff8da788 READ of size 4 at 0xf0d05df4 thread T0 #0 0x8681a2d in gdColorMatch /home/user/php/php-70-asan/ext/gd/libgd/gd_crop.c:348 #1 0x8681a2d in gdImageCropThreshold /home/user/php/php-70-asan/ext/gd/libgd/gd_crop.c:253 #2 0x85b9587 in zif_imagecropauto /home/user/php/php-70-asan/ext/gd/gd.c:4624 #3 0x9a388ac in ZEND_DO_ICALL_SPEC_HANDLER /home/user/php/php-70-asan/Zend/zend_vm_execute.h:586 #4 0x980d06f in execute_ex /home/user/php/php-70-asan/Zend/zend_vm_execute.h:414 #5 0x9b287c5 in zend_execute /home/user/php/php-70-asan/Zend/zend_vm_execute.h:458 #6 0x95e4c3c in zend_execute_scripts /home/user/php/php-70-asan/Zend/zend.c:1427 #7 0x932d58b in php_execute_script /home/user/php/php-70-asan/main/main.c:2494 #8 0x9b31004 in do_cli /home/user/php/php-70-asan/sapi/cli/php_cli.c:974 #9 0x80a6e78 in main /home/user/php/php-70-asan/sapi/cli/php_cli.c:1344 #10 0xf6c7b636 in __libc_start_main (/lib/i386-linux-gnu/libc.so.6+0x18636) #11 0x80a755a (/ram/php-fuzz/phuzzer/php-70-asan/sapi/cli/php+0x80a755a) 0xf0d05df4 is located 92 bytes to the right of 7320-byte region [0xf0d04100,0xf0d05d98) allocated by thread T0 here: #0 0xf727ad06 in malloc (/usr/lib/i386-linux-gnu/libasan.so.2+0x96d06) #1 0x94b68b9 in _emalloc /home/user/php/php-70-asan/Zend/zend_alloc.c:2446 SUMMARY: AddressSanitizer: heap-buffer-overflow /home/user/php/php-70-asan/ext/gd/libgd/gd_crop.c:348 gdColorMatch Shadow bytes around the buggy address: 0x3e1a0b60: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 0x3e1a0b70: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 0x3e1a0b80: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 0x3e1a0b90: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 0x3e1a0ba0: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 =>0x3e1a0bb0: 00 00 00 fa fa fa fa fa fa fa fa fa fa fa[fa]fa 0x3e1a0bc0: fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa 0x3e1a0bd0: fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa 0x3e1a0be0: fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa 0x3e1a0bf0: fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa 0x3e1a0c00: fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa Shadow byte legend (one shadow byte represents 8 application bytes): Addressable: 00 Partially addressable: 01 02 03 04 05 06 07 Heap left redzone: fa Heap right redzone: fb Freed heap region: fd Stack left redzone: f1 Stack mid redzone: f2 Stack right redzone: f3 Stack partial redzone: f4 Stack after return: f5 Stack use after scope: f8 Global redzone: f9 Global init order: f6 Poisoned by user: f7 Container overflow: fc Array cookie: ac Intra object redzone: bb ASan internal: fe ==23837==ABORTING PatchesPull RequestsHistoryAllCommentsChangesGit/SVN commits
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I can't see if the patch was attached, I'm typing it as a comment here just in case: diff --git a/ext/gd/gd.c b/ext/gd/gd.c index d863523..8c88474 100644 --- a/ext/gd/gd.c +++ b/ext/gd/gd.c @@ -4617,7 +4617,7 @@ PHP_FUNCTION(imagecropauto) break; case GD_CROP_THRESHOLD: - if (color < 0) { + if (color < 0 || (!gdImageTrueColor(im) && color >= gdImageColorsTotal(im))) { php_error_docref(NULL, E_WARNING, "Color argument missing with threshold mode"); RETURN_FALSE; }