On Thu, 2023-01-12 at 12:45 -0500, Mimi Zohar wrote: > On Thu, 2023-01-12 at 13:36 +0100, Roberto Sassu wrote: > > On Wed, 2023-01-11 at 09:25 -0500, Paul Moore wrote: > > > On Wed, Jan 11, 2023 at 4:31 AM Roberto Sassu > > > <roberto.sassu@xxxxxxxxxxxxxxx> wrote: > > > > On Fri, 2023-01-06 at 16:14 -0500, Paul Moore wrote: > > > > > On Wed, Dec 21, 2022 at 9:10 AM Roberto Sassu > > > > > <roberto.sassu@xxxxxxxxxxxxxxx> wrote: > > > > > > From: Roberto Sassu <roberto.sassu@xxxxxxxxxx> > > > > > > > > > > > > Commit 98de59bfe4b2f ("take calculation of final prot in > > > > > > security_mmap_file() into a helper") moved the code to update prot with the > > > > > > actual protection flags to be granted to the requestor by the kernel to a > > > > > > helper called mmap_prot(). However, the patch didn't update the argument > > > > > > passed to ima_file_mmap(), making it receive the requested prot instead of > > > > > > the final computed prot. > > > > > > > > > > > > A possible consequence is that files mmapped as executable might not be > > > > > > measured/appraised if PROT_EXEC is not requested but subsequently added in > > > > > > the final prot. > > > > > > > > > > > > Replace prot with mmap_prot(file, prot) as the second argument of > > > > > > ima_file_mmap() to restore the original behavior. > > > > > > > > > > > > Cc: stable@xxxxxxxxxxxxxxx > > > > > > Fixes: 98de59bfe4b2 ("take calculation of final prot in security_mmap_file() into a helper") > > > > > > Signed-off-by: Roberto Sassu <roberto.sassu@xxxxxxxxxx> > > > > > > --- > > > > > > security/security.c | 2 +- > > > > > > 1 file changed, 1 insertion(+), 1 deletion(-) > > > > > > > > > > > > diff --git a/security/security.c b/security/security.c > > > > > > index d1571900a8c7..0d2359d588a1 100644 > > > > > > --- a/security/security.c > > > > > > +++ b/security/security.c > > > > > > @@ -1666,7 +1666,7 @@ int security_mmap_file(struct file *file, unsigned long prot, > > > > > > mmap_prot(file, prot), flags); > > > > > > if (ret) > > > > > > return ret; > > > > > > - return ima_file_mmap(file, prot); > > > > > > + return ima_file_mmap(file, mmap_prot(file, prot)); > > > > > > } > > > > > > > > > > This seems like a reasonable fix, although as the original commit is > > > > > ~10 years old at this point I am a little concerned about the impact > > > > > this might have on IMA. Mimi, what do you think? > > > > As a user, I probably would like to know that my system is not > > measuring what it is supposed to measure. The rule: > > Agreed, that it is measuring what it is supposed to measure. > > > measure func=MMAP_CHECK mask=MAY_EXEC > > > > is looking for executable code mapped in memory. If it is requested by > > the application or the kernel, probably it does not make too much > > difference from the perspective of measurement goals. > > Currently, it's limited to measuring file's being mmapped. From what I > can tell from looking at the code, additional measurements would be > included when "current->personality & READ_IMPLIES_EXEC". Yes, I developed a small program to see the differences: void main() { struct stat st; personality(READ_IMPLIES_EXEC); stat("test-file", &st); int fd = open("test-file", O_RDONLY); mmap(0, st.st_size, PROT_READ, MAP_PRIVATE, fd, 0); } Without the patch, the test-file measurement does not appear. > > If we add a new policy keyword, existing policies would not be updated > > unless the system administrator notices it. If a remote attestation > > fails, the administrator has to look into it. > > Verifying the measurement list against a TPM quote should work > regardless of additional measurements. The attestation server, > however, should also check for unknown files. > > > Maybe we can introduce a new hook called MMAP_CHECK_REQ, so that an > > administrator could change the policy to have the current behavior, if > > the administrator wishes so. > > Agreed, for backwards compatibility this would be good. Would you > support it afterward transitioning IMA to an LSM? Yes, I have a patch to align ima_file_mmap() with the mmap_file() hook definition: -int ima_file_mmap(struct file *file, unsigned long prot) +int ima_file_mmap(struct file *file, unsigned long reqprot, + unsigned long prot, unsigned long flags) This would have also fixed the issue. But for backporting, I did a standalone patch. I noticed that Kees found this as well: -int ima_file_mmap(struct file *file, unsigned long prot) +static int ima_file_mmap(struct file *file, unsigned long reqprot, + unsigned long prot, unsigned long flags) { u32 secid; - if (file && (prot & PROT_EXEC)) { + if (file && (reqprot & PROT_EXEC)) { but from the history I saw that the original intent was to consider prot, not reqprot. > However "_REQ" could mean either requested or required. It was to recall reqprot. I could rename to MMAP_CHECK_REQPROT. Thanks Roberto > > > > > Beyond that, my only other comment would be to only call mmap_prot() > > > > > once and cache the results in a local variable. You could also fix up > > > > > some of the ugly indentation crimes in security_mmap_file() while you > > > > > are at it, e.g. something like this: > > > > > > > > Hi Paul > > > > > > > > thanks for the comments. With the patch set to move IMA and EVM to the > > > > LSM infrastructure we will be back to calling mmap_prot() only once, > > > > but I guess we could do anyway, as the patch (if accepted) would be > > > > likely backported to stable kernels. > > > > > > I think there is value in fixing this now and keeping it separate from > > > the IMA-to-LSM work as they really are disjoint. > > >