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Kees Cook
cfba1d1b61
The new GCC 15 warning -Wunterminated-string-initialization reports:
In file included from drivers/net/ethernet/mellanox/mlx5/core/en.h:55,
from drivers/net/ethernet/mellanox/mlx5/core/en_stats.c:34:
drivers/net/ethernet/mellanox/mlx5/core/en_stats.h:57:46: warning: initializer-string for array of 'char' truncates NUL terminator but destination lacks 'nonstring' attribute (33 chars into 32 available) [-Wunterminated-string-initialization]
57 | #define MLX5E_DECLARE_PTP_RQ_STAT(type, fld) "ptp_rq%d_"#fld, offsetof(type, fld)
| ^~~~~~~~~~~
drivers/net/ethernet/mellanox/mlx5/core/en_stats.c:2279:11: note: in expansion of macro 'MLX5E_DECLARE_PTP_RQ_STAT'
2279 | { MLX5E_DECLARE_PTP_RQ_STAT(struct mlx5e_rq_stats, csum_complete_tail_slow) },
| ^~~~~~~~~~~~~~~~~~~~~~~~~
This stat string is being used in ethtool_sprintf(), so it must be a
valid NUL-terminated string. Currently the string lacks the final NUL
byte (as GCC warns), but by absolute luck, the next byte in memory is a
space (decimal 32) followed by a NUL. "format" is immediately followed
by little-endian size_t:
struct counter_desc {
char format[32]; /* 0 32 */
size_t offset; /* 32 8 */
};
The "offset" member is populated by the stats member offset:
#define MLX5E_DECLARE_PTP_RQ_STAT(type, fld) "ptp_rq%d_"#fld, offsetof(type, fld)
which for this struct mlx5e_rq_stats member, csum_complete_tail_slow, is
32, or space, and then the rest of the "offset" bytes are NULs.
struct mlx5e_rq_stats {
...
u64 csum_complete_tail_slow; /* 32 8 */
The use of vsnprintf(), within ethtool_sprintf(), reads past the end of
"format" and sees the format string as "ptp_rq%d_csum_complete_tail_slow ",
with %d getting resolved by MLX5E_PTP_CHANNEL_IX (value 0):
ethtool_sprintf(data, ptp_rq_stats_desc[i].format,
MLX5E_PTP_CHANNEL_IX);
With an output result of "ptp_rq0_csum_complete_tail_slow", which gets
precisely truncated to 31 characters with a trailing NUL.
So, instead of accidentally getting this correct due to the NUL bytes
at the end of the size_t that happens to follow the format string, just
make the string initializer 1 byte shorter by replacing "%d" with "0",
since MLX5E_PTP_CHANNEL_IX is already hard-coded. This results in no
initializer truncation and no need to call sprintf().
Signed-off-by: Kees Cook <kees@kernel.org>
Reviewed-by: Dragos Tatulea <dtatulea@nvidia.com>
Link: https://patch.msgid.link/20250416020109.work.297-kees@kernel.org
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
Linux kernel
============
There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.
In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``. The formatted documentation can also be read online at:
https://www.kernel.org/doc/html/latest/
There are various text files in the Documentation/ subdirectory,
several of them using the reStructuredText markup notation.
Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.