lavc/bitstream: avoid UB in bits_{read,peek}_signed(0)

bits_*_signed(0) will currently invoke an undefined shift by 8 * sizeof(int). Add bits_*_signed_nz() that only works for n>0, analogous to bits_read_nz(). Add an explicit check for n=0 in bits_*_signed().

Anton Khirnov committed 3 years ago

Commit 0b333101 parent bf23d533 files · +39 −3Browse files

Unified · Split

3 files

libavcodec/bitstream.h +4 −0
libavcodec/bitstream_template.h +34 −2
libavcodec/get_bits.h +1 −1

libavcodec/bitstream.h+4−0

@@ -89,9 +89,11 @@ · 88 unmodified lines
89	89	# define bits_read_63 bits_read_63_le
90	90	# define bits_read_64 bits_read_64_le
91	91	# define bits_read_signed bits_read_signed_le
	92	+# define bits_read_signed_nz bits_read_signed_nz_le
92	93	# define bits_peek_nz bits_peek_nz_le
93	94	# define bits_peek bits_peek_le
94	95	# define bits_peek_signed bits_peek_signed_le
	96	+# define bits_peek_signed_nz bits_peek_signed_nz_le
95	97	# define bits_skip bits_skip_le
96	98	# define bits_seek bits_seek_le
97	99	# define bits_align bits_align_le
@@ -115,9 +117,11 @@ · 17 unmodified lines
115	117	# define bits_read_63 bits_read_63_be
116	118	# define bits_read_64 bits_read_64_be
117	119	# define bits_read_signed bits_read_signed_be
	120	+# define bits_read_signed_nz bits_read_signed_nz_be
118	121	# define bits_peek_nz bits_peek_nz_be
119	122	# define bits_peek bits_peek_be
120	123	# define bits_peek_signed bits_peek_signed_be
	124	+# define bits_peek_signed_nz bits_peek_signed_nz_be
121	125	# define bits_skip bits_skip_be
122	126	# define bits_seek bits_seek_be
123	127	# define bits_align bits_align_be

libavcodec/bitstream_template.h+34−2

@@ -290,13 +290,29 @@ static inline uint64_t BS_FUNC(read_64)(BSCTX *bc, unsigned int n) · 289 unmodified lines
290	290	return BS_FUNC(read_63)(bc, n);
291	291	}
292	292
	293	+/**
	294	+ * Return n bits from the buffer as a signed integer, n has to be in the 1-32
	295	+ * range. May be faster than bits_read_signed() when n is not a compile-time
	296	+ * constant and is known to be non-zero;
	297	+ */
	298	+static inline int32_t BS_FUNC(read_signed_nz)(BSCTX *bc, unsigned int n)
	299	+{
	300	+ av_assert2(n > 0 && n <= 32);
	301	+ return sign_extend(BS_FUNC(read_nz)(bc, n), n);
	302	+}
	303	+
293	304	/**
294	305	* Return n bits from the buffer as a signed integer.
295	306	* n has to be in the 0-32 range.
296	307	*/
297	308	static inline int32_t BS_FUNC(read_signed)(BSCTX *bc, unsigned int n)
298	309	{
299		− return sign_extend(BS_FUNC(read)(bc, n), n);
	310	+ av_assert2(n <= 32);
	311	+
	312	+ if (!n)
	313	+ return 0;
	314	+
	315	+ return BS_FUNC(read_signed_nz)(bc, n);
300	316	}
301	317
302	318	/**
@@ -327,6 +343,17 @@ static inline uint32_t BS_FUNC(peek)(BSCTX *bc, unsigned int n) · 24 unmodified lines
327	343	return BS_FUNC(peek_nz)(bc, n);
328	344	}
329	345
	346	+/**
	347	+ * Return n bits from the buffer as a signed integer, do not change the buffer
	348	+ * state. n has to be in the 1-32 range. May be faster than bits_peek_signed()
	349	+ * when n is not a compile-time constant and is known to be non-zero;
	350	+ */
	351	+static inline int BS_FUNC(peek_signed_nz)(BSCTX *bc, unsigned int n)
	352	+{
	353	+ av_assert2(n > 0 && n <= 32);
	354	+ return sign_extend(BS_FUNC(peek_nz)(bc, n), n);
	355	+}
	356	+
330	357	/**
331	358	* Return n bits from the buffer as a signed integer,
332	359	* do not change the buffer state.
@@ -334,7 +361,12 @@ static inline uint32_t BS_FUNC(peek)(BSCTX *bc, unsigned int n) · 1 unmodified line
334	361	*/
335	362	static inline int BS_FUNC(peek_signed)(BSCTX *bc, unsigned int n)
336	363	{
337		− return sign_extend(BS_FUNC(peek)(bc, n), n);
	364	+ av_assert2(n <= 32);
	365	+
	366	+ if (!n)
	367	+ return 0;
	368	+
	369	+ return BS_FUNC(peek_signed_nz)(bc, n);
338	370	}
339	371
340	372	/**

libavcodec/get_bits.h+1−1

@@ -85,7 +85,7 @@ typedef BitstreamContext GetBitContext; · 84 unmodified lines
85	85	#define get_bits1 bits_read_bit
86	86	#define get_bits64 bits_read_64
87	87	#define get_xbits bits_read_xbits
88		−#define get_sbits bits_read_signed
	88	+#define get_sbits bits_read_signed_nz
89	89	#define get_sbits_long bits_read_signed
90	90	#define show_bits bits_peek
91	91	#define show_bits_long bits_peek

lavc/bitstream: avoid UB in bits_{read,peek}_signed(0)

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