gfs2: Prevent recursive memory reclaim

Vulnerability Description

In the Linux kernel, the following vulnerability has been resolved: gfs2: Prevent recursive memory reclaim Function new_inode() returns a new inode with inode->i_mapping->gfp_mask set to GFP_HIGHUSER_MOVABLE. This value includes the __GFP_FS flag, so allocations in that address space can recurse into filesystem memory reclaim. We don't want that to happen because it can consume a significant amount of stack memory. Worse than that is that it can also deadlock: for example, in several places, gfs2_unstuff_dinode() is called inside filesystem transactions. This calls filemap_grab_folio(), which can allocate a new folio, which can trigger memory reclaim. If memory reclaim recurses into the filesystem and starts another transaction, a deadlock will ensue. To fix these kinds of problems, prevent memory reclaim from recursing into filesystem code by making sure that the gfp_mask of inode address spaces doesn't include __GFP_FS. The "meta" and resource group address spaces were already using GFP_NOFS as their gfp_mask (which doesn't include __GFP_FS). The default value of GFP_HIGHUSER_MOVABLE is less restrictive than GFP_NOFS, though. To avoid being overly limiting, use the default value and only knock off the __GFP_FS flag. I'm not sure if this will actually make a difference, but it also shouldn't hurt. This patch is loosely based on commit ad22c7a043c2 ("xfs: prevent stack overflows from page cache allocation"). Fixes xfstest generic/273.

References

• https://git.kernel.org/stable/c/edb2b255618621dc83d0ec23150e16b2c697077f
• https://git.kernel.org/stable/c/9c0960ed112398bdb6c60ccf6e6b583bc59acede
• https://git.kernel.org/stable/c/49e7347f4644d031306d56cb4d51e467cbdcbc69
• https://git.kernel.org/stable/c/2c5f4a53476e3cab70adc77b38942c066bd2c17c