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author | Gustavo A. R. Silva <gustavo@embeddedor.com> | 2020-01-21 11:21:38 -0600 |
---|---|---|
committer | Greg Kroah-Hartman <gregkh@linuxfoundation.org> | 2020-01-23 19:22:49 +0100 |
commit | 85f4c95172d606dd66f7ee1fa50c45a245535ffd (patch) | |
tree | 5f4a8806668484c6a48c508c33036a499091a5e9 | |
parent | 1ddeb5a74ab6941dfd310b73c8554c393c70c2ef (diff) | |
download | linux-85f4c95172d606dd66f7ee1fa50c45a245535ffd.tar.gz linux-85f4c95172d606dd66f7ee1fa50c45a245535ffd.tar.bz2 linux-85f4c95172d606dd66f7ee1fa50c45a245535ffd.zip |
tty: n_hdlc: Use flexible-array member and struct_size() helper
Old code in the kernel uses 1-byte and 0-byte arrays to indicate the
presence of a "variable length array":
struct something {
int length;
u8 data[1];
};
struct something *instance;
instance = kmalloc(sizeof(*instance) + size, GFP_KERNEL);
instance->length = size;
memcpy(instance->data, source, size);
There is also 0-byte arrays. Both cases pose confusion for things like
sizeof(), CONFIG_FORTIFY_SOURCE, etc.[1] Instead, the preferred mechanism
to declare variable-length types such as the one above is a flexible array
member[2] which need to be the last member of a structure and empty-sized:
struct something {
int stuff;
u8 data[];
};
Also, by making use of the mechanism above, we will get a compiler warning
in case the flexible array does not occur last in the structure, which
will help us prevent some kind of undefined behavior bugs from being
inadvertenly introduced[3] to the codebase from now on.
Lastly, make use of the struct_size() helper to safely calculate the
allocation size for instances of struct n_hdlc_buf and avoid any potential
type mistakes[4][5].
[1] https://github.com/KSPP/linux/issues/21
[2] https://gcc.gnu.org/onlinedocs/gcc/Zero-Length.html
[3] commit 76497732932f ("cxgb3/l2t: Fix undefined behaviour")
[4] https://lore.kernel.org/lkml/60e14fb7-8596-e21c-f4be-546ce39e7bdb@embeddedor.com/
[5] commit 553d66cb1e86 ("iommu/vt-d: Use struct_size() helper")
Signed-off-by: Gustavo A. R. Silva <gustavo@embeddedor.com>
Reviewed-by: Jiri Slaby <jslaby@suse.cz>
Link: https://lore.kernel.org/r/20200121172138.GA3162@embeddedor
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
-rw-r--r-- | drivers/tty/n_hdlc.c | 11 |
1 files changed, 5 insertions, 6 deletions
diff --git a/drivers/tty/n_hdlc.c b/drivers/tty/n_hdlc.c index 98361acd3053..27b506bf03ce 100644 --- a/drivers/tty/n_hdlc.c +++ b/drivers/tty/n_hdlc.c @@ -115,11 +115,9 @@ struct n_hdlc_buf { struct list_head list_item; int count; - char buf[1]; + char buf[]; }; -#define N_HDLC_BUF_SIZE (sizeof(struct n_hdlc_buf) + maxframe) - struct n_hdlc_buf_list { struct list_head list; int count; @@ -524,7 +522,8 @@ static void n_hdlc_tty_receive(struct tty_struct *tty, const __u8 *data, /* no buffers in free list, attempt to allocate another rx buffer */ /* unless the maximum count has been reached */ if (n_hdlc->rx_buf_list.count < MAX_RX_BUF_COUNT) - buf = kmalloc(N_HDLC_BUF_SIZE, GFP_ATOMIC); + buf = kmalloc(struct_size(buf, buf, maxframe), + GFP_ATOMIC); } if (!buf) { @@ -853,7 +852,7 @@ static struct n_hdlc *n_hdlc_alloc(void) /* allocate free rx buffer list */ for(i=0;i<DEFAULT_RX_BUF_COUNT;i++) { - buf = kmalloc(N_HDLC_BUF_SIZE, GFP_KERNEL); + buf = kmalloc(struct_size(buf, buf, maxframe), GFP_KERNEL); if (buf) n_hdlc_buf_put(&n_hdlc->rx_free_buf_list,buf); else if (debuglevel >= DEBUG_LEVEL_INFO) @@ -862,7 +861,7 @@ static struct n_hdlc *n_hdlc_alloc(void) /* allocate free tx buffer list */ for(i=0;i<DEFAULT_TX_BUF_COUNT;i++) { - buf = kmalloc(N_HDLC_BUF_SIZE, GFP_KERNEL); + buf = kmalloc(struct_size(buf, buf, maxframe), GFP_KERNEL); if (buf) n_hdlc_buf_put(&n_hdlc->tx_free_buf_list,buf); else if (debuglevel >= DEBUG_LEVEL_INFO) |