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Kees Cook
2dca62902e
commit e4c8b46b92 upstream.
As done for kmalloc_obj*(), introduce a type-aware allocator for flexible
arrays, which may also have "counted_by" annotations:
ptr = kmalloc(struct_size(ptr, flex_member, count), gfp);
becomes:
ptr = kmalloc_flex(*ptr, flex_member, count, gfp);
The internal use of __flex_counter() allows for automatically setting
the counter member of a struct's flexible array member when it has
been annotated with __counted_by(), avoiding any missed early size
initializations while __counted_by() annotations are added to the
kernel. Additionally, this also checks for "too large" allocations based
on the type size of the counter variable. For example:
if (count > type_max(ptr->flex_counter))
fail...;
size = struct_size(ptr, flex_member, count);
ptr = kmalloc(size, gfp);
if (!ptr)
fail...;
ptr->flex_counter = count;
becomes (n.b. unchanged from earlier example):
ptr = kmalloc_flex(*ptr, flex_member, count, gfp);
if (!ptr)
fail...;
ptr->flex_counter = count;
Note that manual initialization of the flexible array counter is still
required (at some point) after allocation as not all compiler versions
support the __counted_by annotation yet. But doing it internally makes
sure they cannot be missed when __counted_by _is_ available, meaning
that the bounds checker will not trip due to the lack of "early enough"
initializations that used to work before enabling the stricter bounds
checking. For example:
ptr = kmalloc_flex(*ptr, flex_member, count, gfp);
fill(ptr->flex, count);
ptr->flex_count = count;
This works correctly before adding a __counted_by annotation (since
nothing is checking ptr->flex accesses against ptr->flex_count). After
adding the annotation, the bounds sanitizer would trip during fill()
because ptr->flex_count wasn't set yet. But with kmalloc_flex() setting
ptr->flex_count internally at allocation time, the existing code works
without needing to move the ptr->flex_count assignment before the call
to fill(). (This has been a stumbling block for __counted_by adoption.)
Link: https://patch.msgid.link/20251203233036.3212363-4-kees@kernel.org
Acked-by: Vlastimil Babka <vbabka@suse.cz>
Signed-off-by: Kees Cook <kees@kernel.org>
[Backport-notes: Removed the actual flex counter handling. That's a new
feature, which isn't necessary for just adding the new allocation APIs
to get backports to apply cleanly. Also, the allocation-time overflow
check in the upstream commit was reverted upstream.]
Signed-off-by: Eric Biggers <ebiggers@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Linux kernel
============
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Documentation/admin-guide/README.rst first.
In order to build the documentation, use ``make htmldocs`` or
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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.