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https://github.com/libexif/libexif/commit/75aa73267fdb1e0ebfbc00369e7312bac43d0566.patch |
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From 75aa73267fdb1e0ebfbc00369e7312bac43d0566 Mon Sep 17 00:00:00 2001 |
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From: Marcus Meissner <meissner@suse.de> |
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Date: Sat, 18 Jan 2020 09:29:42 +0100 |
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Subject: [PATCH] fix CVE-2019-9278 |
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avoid the use of unsafe integer overflow checking constructs (unsigned integer operations cannot overflow, so "u1 + u2 > u1" can be optimized away) |
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check for the actual sizes, which should also handle the overflows |
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document other places google patched, but do not seem relevant due to other restrictions |
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fixes https://github.com/libexif/libexif/issues/26 |
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--- |
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libexif/exif-data.c | 28 ++++++++++++++++++---------- |
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1 file changed, 18 insertions(+), 10 deletions(-) |
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diff --git libexif/exif-data.c libexif/exif-data.c |
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index a6f9c94..6332cd1 100644 |
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--- libexif/exif-data.c |
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+++ libexif/exif-data.c |
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@@ -192,9 +192,15 @@ exif_data_load_data_entry (ExifData *data, ExifEntry *entry, |
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doff = offset + 8; |
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|
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/* Sanity checks */ |
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- if ((doff + s < doff) || (doff + s < s) || (doff + s > size)) { |
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+ if (doff >= size) { |
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exif_log (data->priv->log, EXIF_LOG_CODE_DEBUG, "ExifData", |
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- "Tag data past end of buffer (%u > %u)", doff+s, size); |
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+ "Tag starts past end of buffer (%u > %u)", doff, size); |
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+ return 0; |
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+ } |
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+ |
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+ if (s > size - doff) { |
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+ exif_log (data->priv->log, EXIF_LOG_CODE_DEBUG, "ExifData", |
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+ "Tag data goes past end of buffer (%u > %u)", doff+s, size); |
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return 0; |
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} |
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|
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@@ -315,13 +321,14 @@ exif_data_load_data_thumbnail (ExifData *data, const unsigned char *d, |
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unsigned int ds, ExifLong o, ExifLong s) |
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{ |
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/* Sanity checks */ |
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- if ((o + s < o) || (o + s < s) || (o + s > ds) || (o > ds)) { |
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- exif_log (data->priv->log, EXIF_LOG_CODE_DEBUG, "ExifData", |
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- "Bogus thumbnail offset (%u) or size (%u).", |
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- o, s); |
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+ if (o >= ds) { |
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+ exif_log (data->priv->log, EXIF_LOG_CODE_DEBUG, "ExifData", "Bogus thumbnail offset (%u).", o); |
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+ return; |
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+ } |
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+ if (s > ds - o) { |
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+ exif_log (data->priv->log, EXIF_LOG_CODE_DEBUG, "ExifData", "Bogus thumbnail size (%u), max would be %u.", s, ds-o); |
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return; |
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} |
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- |
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if (data->data) |
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exif_mem_free (data->priv->mem, data->data); |
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if (!(data->data = exif_data_alloc (data, s))) { |
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@@ -947,7 +954,7 @@ exif_data_load_data (ExifData *data, const unsigned char *d_orig, |
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exif_log (data->priv->log, EXIF_LOG_CODE_DEBUG, "ExifData", |
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"IFD 0 at %i.", (int) offset); |
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|
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- /* Sanity check the offset, being careful about overflow */ |
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+ /* ds is restricted to 16 bit above, so offset is restricted too, and offset+8 should not overflow. */ |
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if (offset > ds || offset + 6 + 2 > ds) |
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return; |
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|
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@@ -956,6 +963,7 @@ exif_data_load_data (ExifData *data, const unsigned char *d_orig, |
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/* IFD 1 offset */ |
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n = exif_get_short (d + 6 + offset, data->priv->order); |
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+ /* offset < 2<<16, n is 16 bit at most, so this op will not overflow */ |
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if (offset + 6 + 2 + 12 * n + 4 > ds) |
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return; |
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|
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@@ -964,8 +972,8 @@ exif_data_load_data (ExifData *data, const unsigned char *d_orig, |
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exif_log (data->priv->log, EXIF_LOG_CODE_DEBUG, "ExifData", |
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"IFD 1 at %i.", (int) offset); |
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|
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- /* Sanity check. */ |
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- if (offset > ds || offset + 6 > ds) { |
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+ /* Sanity check. ds is ensured to be above 6 above, offset is 16bit */ |
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+ if (offset > ds - 6) { |
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exif_log (data->priv->log, EXIF_LOG_CODE_CORRUPT_DATA, |
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"ExifData", "Bogus offset of IFD1."); |
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} else { |