maple_tree: fix MA_STATE_PREALLOC flag in mas_preallocate()

Vulnerability Description

In the Linux kernel, the following vulnerability has been resolved: maple_tree: fix MA_STATE_PREALLOC flag in mas_preallocate() Temporarily clear the preallocation flag when explicitly requesting allocations. Pre-existing allocations are already counted against the request through mas_node_count_gfp(), but the allocations will not happen if the MA_STATE_PREALLOC flag is set. This flag is meant to avoid re-allocating in bulk allocation mode, and to detect issues with preallocation calculations. The MA_STATE_PREALLOC flag should also always be set on zero allocations so that detection of underflow allocations will print a WARN_ON() during consumption. User visible effect of this flaw is a WARN_ON() followed by a null pointer dereference when subsequent requests for larger number of nodes is ignored, such as the vma merge retry in mmap_region() caused by drivers altering the vma flags (which happens in v6.6, at least)

References

• https://git.kernel.org/stable/c/d69cd64bd5af41c6fd409313504089970edaf02f
• https://git.kernel.org/stable/c/e63032e66bca1d06e600033f3369ba3db3af0870
• https://git.kernel.org/stable/c/cf95f8426f889949b738f51ffcd72884411f3a6a
• https://git.kernel.org/stable/c/9e32f4700867abbd5d19abfcf698dbd0d2ce36a4
• https://git.kernel.org/stable/c/fba46a5d83ca8decb338722fb4899026d8d9ead2