[lttng-dev] [PATCH lttng-tools 3/3] Fix: Generation of bytecode longer than 32768 bytes fails

[Mathieu Desnoyers]

* Christian Babeux (christian.babeux at efficios.com) wrote:
> The bytecode buffer length field is currently limited to a uint16_t.
> A larger buffer, lttng_filter_bytecode_alloc, is the underlying storage
> for the bytecode.
> 
> The current allocation policy dictate that the alloc buffer size must be
> doubled everytime the bytecode size plus padding exceeds its capacity.
> 
> A problem arise when generating bytecode larger than 32768 bytes.
> 
> e.g.:
> 
> Legend
> * required_len: new bytecode len
> * old_len: current alloc_len
> * new_len: new alloc_len
> 
> src/bin/lttng/lttng enable-event event:bla -s foo -u --filter "`perl -e 'print "intfield" . " && 1" x2730'`"
> UST event ust_tests_hello:tptest created in channel channel0
> [debug liblttng-ctl] Generating IR... [debug liblttng-ctl] done
> [debug liblttng-ctl] Validating IR... [debug liblttng-ctl] done
> [debug liblttng-ctl] Generating bytecode... required_len = 11, old_len = 4, new_len = 16
> required_len = 7, old_len = 4, new_len = 8
> required_len = 16, old_len = 8, new_len = 16
> required_len = 19, old_len = 16, new_len = 32
> required_len = 40, old_len = 32, new_len = 64
> required_len = 67, old_len = 64, new_len = 128
> required_len = 136, old_len = 128, new_len = 256
> required_len = 259, old_len = 256, new_len = 512
> required_len = 520, old_len = 512, new_len = 1024
> required_len = 1027, old_len = 1024, new_len = 2048
> required_len = 2056, old_len = 2048, new_len = 4096
> required_len = 4099, old_len = 4096, new_len = 8192
> required_len = 8200, old_len = 8192, new_len = 16384
> required_len = 16387, old_len = 16384, new_len = 32768
> required_len = 32776, old_len = 32768, new_len = 65536 <-- Overflow 16-bits
> Generate bytecode error
> Error: Error setting filter
> 
> The last new_len exceed the range of 16-bits values. In order to support
> the largest bytecode length (65535), the underlying alloc buffer len must
> be able to store more than 65535. Fix this by using a uint32_t for alloc_len.
> 
> Also, add a check to ensure that a bytecode longer than LTTNG_FILTER_MAX_LEN
> (65535) bytes can't be generated.
> 
> Signed-off-by: Christian Babeux <christian.babeux at efficios.com>

Acked-by: Mathieu Desnoyers <mathieu.desnoyers at efficios.com>

> ---
>  src/lib/lttng-ctl/filter/filter-bytecode.h                  | 2 +-
>  src/lib/lttng-ctl/filter/filter-visitor-generate-bytecode.c | 5 +++--
>  2 files changed, 4 insertions(+), 3 deletions(-)
> 
> diff --git a/src/lib/lttng-ctl/filter/filter-bytecode.h b/src/lib/lttng-ctl/filter/filter-bytecode.h
> index 5d2559d..d364ee2 100644
> --- a/src/lib/lttng-ctl/filter/filter-bytecode.h
> +++ b/src/lib/lttng-ctl/filter/filter-bytecode.h
> @@ -176,7 +176,7 @@ struct return_op {
>  } __attribute__((packed));
>  
>  struct lttng_filter_bytecode_alloc {
> -	uint16_t alloc_len;
> +	uint32_t alloc_len;
>  	struct lttng_filter_bytecode b;
>  };
>  
> diff --git a/src/lib/lttng-ctl/filter/filter-visitor-generate-bytecode.c b/src/lib/lttng-ctl/filter/filter-visitor-generate-bytecode.c
> index 71da21c..98f8375 100644
> --- a/src/lib/lttng-ctl/filter/filter-visitor-generate-bytecode.c
> +++ b/src/lib/lttng-ctl/filter/filter-visitor-generate-bytecode.c
> @@ -95,14 +95,15 @@ int32_t bytecode_reserve(struct lttng_filter_bytecode_alloc **fb, uint32_t align
>  	int32_t ret;
>  	uint32_t padding = offset_align((*fb)->b.len, align);
>  
> +	if ((*fb)->b.len + padding + len > LTTNG_FILTER_MAX_LEN)
> +		return -EINVAL;
> +
>  	if ((*fb)->b.len + padding + len > (*fb)->alloc_len) {
>  		uint32_t new_len =
>  			max_t(uint32_t, 1U << get_count_order((*fb)->b.len + padding + len),
>  				(*fb)->alloc_len << 1);
>  		uint32_t old_len = (*fb)->alloc_len;
>  
> -		if (new_len > 0xFFFF)
> -			return -EINVAL;
>  		*fb = realloc(*fb, sizeof(struct lttng_filter_bytecode_alloc) + new_len);
>  		if (!*fb)
>  			return -ENOMEM;
> -- 
> 1.7.11.4
> 

-- 
Mathieu Desnoyers
Operating System Efficiency R&D Consultant
EfficiOS Inc.
http://www.efficios.com